Genetics - Mind Map

Genetics

Genetic Variation & Errors in Meiosis

Genetic variation = variation in DNA sequence in our genomes

Genetic variation is ensured in crossing over and independent assortment

Crossing over: occurs during prophase I, genetic material is exchanged between maternal and paternal chromosomes

Independent assortment: occurs during metaphase I, gametes are created and carry different combinations of maternal and paternal chromosomes

Errors in meiosis caused by non-disjunction or caused by changes in chromosome structure

Non-disjunction: when chromosomes don't separate correctly in meiosis and result in abnormal number of chromosomes

Euploidy (correct number of chromosomes), aneuploidy (incorrect number of chromosomes), monosomy = missing chromosome, polysomy = additional chromosome(s)

Anaphase I: Homologous chromosome pairs don't separate to opposite poles, no normal gametes

Anaphase II: sister chromatids don't separate to opposite poles, half of gametes have correct chromosome number

Extra chromosome 21 (Trisomy 21) = Down Syndrome, 1 sex chromosome = Turner Syndrome (only in females), Extra Y chromosome = Jacob's Syndrome (only in males)

Chromosome structure errors: During crossing over the chemical bonds holding the DNA are broken and reformed

chromosomes don't reform properly or non-homologous pairs cross over

Deletion: piece of chromosome is deleted

Duplication: section of chromosome is repeated (appears 2 or more times in a row)

Inversion: section of chromosome reattaches to chromatid in wrong orientation - DNA sequence is reversed

Translocation: Section of 1 chromosome becomes attached to a different chromosome

Genetic Testing: type of medical test that identifies change in chromosomes, genes or proteins

Genetic screening in newborns: routine tests are done in hospital as a part of a newborn screening program (not mandatory)

Blood test taken from baby's heel and analyzed for various genetic disorders

Prenatal Genetic Testing: procedures and tests performed on the fetus to look for genetic-based abnormalities

Gene therapy: experimental treatment to cure genetic disorders

Insert a healthy normal form of a gene into the tissue cells affected, the gene replaces the effects of the mutated gene and restores the function of the protein

Prenatal Genetic Testing

Amniocentesis: Doctor removes a sample of amniotic fluid

Usually done in the 2nd trimester of pregnancy (15-18 weeks)

Recommended to women with risk factors such as age 35 and older, previous child/pregnancy with a birth defect, blood test/ultrasound suggesting a birth defect or a family history of genetic disorders

Chronic Villus Sampling (CVS): The doctor removes a sample of the placenta

Usually done between 10-14 weeks in the pregnancy

Recommended for women with a higher chance of having a baby with a genetic condition/birth defect

Kucha Translucency Screening: A scan that detects chromosomal abnormalities

Genetic counselling

Genetic counsellors help with genetic health, understanding genetic risks and giving information

Meiosis

Human cell has 23 pairs of homologous chromosomes (1 set from paternal, 1 set from maternal)

Diploid organism = homologous pairs (Somatic cells: body cells)

Haploid Organism = 1 set of chromosomes (Reproductive cells: found in reproductive tissue of an organism which produce sperm + egg

Male gamete = sperm, female gamete = ovum

Homologous chromosomes: pair of chromosomes similar in shapes and sizes

Homologous pairs (tetrads) carry genes controlling the same traits

Each locus (position of a gene) = same position on homologues

Autosomes code for majority of offspring's traits, sex chromosomes code for sex of offspring (2 X = female, 1 X + 1 Y = male

Meiosis = process which gamete cells are produced and diploid cells become haploid cells

2 cell divisions (Meiosis I and Meiosis II) and 1 duplication of chromosomes

Meiosis in males = spermatogenesis and produces sperm, meiosis in females = oogenesis and produces ova

Occurs in reproductive tissue, 4 haploid daughter cells are produced from 1 diploid parent cell

Meiosis I

Interphase I = chromosomes replicate, each duplicated chromosome has 2 sister chromatids

Prophase I = 90% of process, chromosomes condense, synapsis occurs, crossing over occurs

Metaphase I = tetrads align on metaphase plate, independent assortment occurs

Anaphase I = Homologous chromosomes separate and move towards poles, sister chromatids remain attached

Telophase I = Each pole has haploid set of chromosomes and cytokinesis occurs and 2 haploid daughter cells form

Meiosis II

Prophase II = chromatin condense to form chromosomes, nuclear membrane breaks down, duplicated centrioles migrate to opposite poles, spindle fibers form

Metaphase II = spindle fibers attach to chromosome centromere and align along equatorial plate, sister chromatids face opposite poles

Anaphase II = centromere splits, sister chromatids are pulled to opposite poles by spindle fibers

Telophase II = nuclear membrane forms around each set of chromatids, spindle fibers appear, cytokinesis occurs and 4 haploid daughter cells are produced

DNA & RNA

Karyotypes = person's set of chromosomes (humans have 23 pairs of chromosomes, 46 in total)

Autosomal vs Sex chromosomes

22 pairs of autosomal (regular) chromosomes and 1 pair of sex chromosomes (XX → female, XY → male)

DNA determines the structure of proteins which are needed because actions of living thins depend on enzymes (proteins)

DNA Structure: 2 molecules arranged into a ladder-like structure (Double Helix)

Made up of millions of tiny subunits called Nucleotides which consist of phosphate group, pentose sugar and nitrogenous base

4 types of nitrogenous bases: Adenine, guanine, thymine and cytosine

Adenine (A) + Thymine (T) form one base pair while Cytosine (C) + Guanine (G) form one base pair

Due to this pairing, the order of the bases in 1 strand determine the order of the bases in the other strand

The bases are arranged in triplets called codons (AGG-CTC-AAG-TCC-TAG)

Phosphate and sugar form the backbone of the DNA molecule and the bases form the "rungs"

Genes: a segment of DNA that codes for a certain trait found at a specific part on a chromosome

Genes code for specific traits because they code for the production of proteins which give us unique phenotypes

DNA replication: Each cell has a copy of DNA that was in the fertilized egg of the zygote and before the cell divides the chromosomes go through DNA replication

Sequencing of nucleotides contain info that works through proteins

Proteins fold into complex 3-D shapes and become key regulators

DNA doesn't leave the nucleus so it uses a messenger (mRNA) to travel the cell (ribosomes via rough ER) to make a protein that travels throughout the body

mRNA leaves the nucleus with the code for a protein

Codons code for proteins such as Amino acids and have stop/start codons

Nucleotide sequence transcribed from DNA to mRNA is the genetic message

RNA has 3 main differences from DNA: RNA = single stranded vs. double stranded, ribose sugar vs. deoxyribose and uracil (U) instead of thymine (T)

Mutations are caused by errors in replications, transcription, cell division or external agents

Mutations in reproductive cells means the gene is apart of the organism and can cause ew traits, non-working proteins, death of organism or structural/functional problems

Mutations in body cells aren't passed down to offspring but can be harmful and have an impaired function of cell

Point Mutation & Frame-Shift Mutation

Point Mutation: 1 change in a nucleotide changes entire meaning

Frame-Shift Mutation: Single base pair is added/deleted, entire strand shifts and entire protein is changed

Patterns of Inheritance and Monohybrid & Dihybrid Cross

Gregor Mendel = botanist in mid 1800s who studied pea plants and noticed that the offspring had different characteristics than their parents

Law of segregation

Inherited traits are determined by 2 alleles of a gene

The alleles segregate into each of the gametes of the parents during meiosis

In fertilization, each offspring contains one allele from each parent

Principles of dominance

Form of trait that's expressed in an individual depends on whether they inherit dominant/recessive alleles

Dominant allele is present, only the dominant for is expressed

In order for the recessive form to be expressed, there needs to be 2 recessive alleles

Vocabulary

Gene: a section of DNA that codes for a particular trait

Alleles: different variations of a gene, rep. using upper (dominant) and lower (recessive) case letter

Dominant: form of trait that always appears when an individual has an allele for it, allele is always expressed

Recessive: form of trait that always appears when an individual has 2 alleles for it, allele is masked in presence of another

Genotype: combination of alleles that code for a trait

Phenotype: appearance of the trait in an organism

Homozygous: genotype made up of the same 2 alleles, 2 upper case alleles = homozygous dominant, 2 lower case alleles = homozygous recessive

Heterozygous: genotype made up of 2 different alleles, uppercase and lower case letter

Punnett Squares

Mendel examined the inheritance one trait at a time (monohybrid cross)

Mendel used a Punnett square to show the multiple combinations of alleles

Complete Dominance: 1 allele is always dominant over the other

Monohybrid cross = single trait crossing, dihybrid cross = inheritance pattern for two traits

Law of Independent Assortment: states that the alleles of one gene sort into gametes independently of the alleles of another gene

Incomplete dominance and Codominance, Polygenic Inheritance & Environmental Effects on Inheritance

Non-Mendelian Genetics: some inherited traits don't follow what Mendel saw

Non-mendelian genetics: incomplete dominance, codominance, polygenic inheritance, modifier genes, multiple alleles and sex-linked traits

Incomplete dominance: neither allele dominates the other, results in heterozygote showing a third phenotype that's in between both traits (blending)

Capital letters carried as superscripts, base letter stays the same

Superscript letter is represented using different letters because alleles = dominant

Codominance: both alleles are fully expressed, results in heterozygote showing a third phenotype with both traits shown (patchy)

Capital letters are carried as superscripts

Polygenic inheritance: the additive effects of 2 or more genes on a single phenotypic characteristic

Multiple genes working together = continuous variation

Controlled by the action of many genes

Modifier genes: a gene can modify the expression of a second gene instead of masking its effects

Environmental factors affect the expression of traits

Temperature can determine whether a gene is turned on or off

Sex-Linked and Multiple Alleles

Linked genes are on the same chromosome

Homologous chromosomes exchange genetic material during synapsis, changing the combination of alleles possible

Traits close together will occur together with higher frequency

Thomas Morgan created a white-eyed male offspring from two red-eyed parents while studying eye colour in fruit flies

Red-eyed female with a white-eyed male = red-eyed F1 offspring

F2 white-eyed flies = male → eye colour is connected to gender lead Morgan to believe eye colour is on X chromosome which is why white eyes is recessive in females and expressed in males

Most sex-linked traits = X-linked (carried on the X chromosome)

X chromosome is much bigger and contains more genes than the Y chromosome

Some sex-linked traits are associated with disorders

Most are found on the X chromosome, Y-linked = rare

Males have a higher risk because they only have one X chromosome

Y-linked inheritance: Y-linked genes can only be transmitted from father to son

The Punnett squares are used to predict the outcome of the sex-linked inheritance

Most disorders = recessive, some = dominant

Carrier = heterozygous female for the trait

Multiple Alleles: interaction of more than 2 alleles for 1 gene

May show multiple patterns (some alleles show complete dominance, others show codominance)

Reproductive Strategies & Technologies

Methods used in Agriculture

Selective Breeding: process of breeding plants and animals for desirable traits

Artificial Insemination: the transfer of processed semen into a female's reproductive tract

Embryo Transfer: fertilizing an egg artificially and transferring it into a recipient female

Assisted reproductive technologies for humans

Artificial Insemination: sperm is collected and concentrated, then introduced into a woman's vagina

In Vitro Fertilization (IVF): immature eggs are retrieved, joined with sperm in a lab and embryos are inserted into the uterus

Option for women with blocked Fallopian tubes

Cloning: Gene cloning, Therapeutic cloning and Reproductive cloning

Gene cloning: manipulating DNA to produce multiple copies of a gene or another segment of DNA in foreign cells

Therapeutic cloning: producing genetically identical cells that are used to treat various diseases, cloned cells grow new tissues and organs

Somatic cell nuclear transfer (SCNT); an egg cell's nucleus is removed and replaced with the nucleus of a somatic cell of a donor

Reproductive cloning: production of cell clones with the aim of producing a genetically identical organism (rarely sucessful)

Also uses SCNT

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