Genes L9 Notes Flashcards
What is population genetics?
• Population genetics:
- Study of the gene pool of a population over time
What is molecular genetics?
• Molecular genetics:
- Study of the molecular structure & function of genes
Describe factors involved in inheritance & gene function
• Inheritance & gene function:
- Transmission of genes
- Genotype vs. phenotype
- Function of genes in organism
What can genetics be applied for? Give examples
• Applications of genetics:
- Human genetics
Breast cancer research
- Plant breeding
Genetically modified crops
–>Creation of semi-dwarf (shorter) wheat in India-> less likely blown over -> more likely to grow.
- Analysis of biological processes
Eg. circadian rhythm ->period gene controlling circadian rhythms discovered ->
can modify rhythms of organisms.
What is a gene?
• What is a gene?
- DNA molecule
Includes transcribed & non-transcribed regions
Includes exons, introns & gene regulatory regions
- Inherited
- Effects phenotype/physical characteristics of organism
- Located on chromosomes
State the normal amount of haploid & diploid chromosomes in humans
• Humans
- N=23 -> 23 haploid chromosomes
- 2N=46 -> 46 diploid chromosomes
Distinguish between the two types of cell division
- Mitosis: Produce -> 2 genetically identical diploid daughter cells 1 cell division Occurs -> All tissues - Meiosis: Produce -> 4 haploid gametes -> from diploid mother cell 2 cell divisions Occurs -> gonads (ovaries/testes) only.
What is the cell cycle?
• Cell cycle:
- Period between -> birth of cell -> division -> 2 daughter cells
Briefly describe Meiosis
• Meiosis: - G2 phase -> S phase cell cycle - Meiosis I: Divides pairs of chromosomes Reductional division (chromosome no. halved) 2 haploid (n) daughter cells - Meiosis II: Divides sister chromatids Equational division 4 haploid gametes
Describe the process of meiosis I
Meiosis I:
»_space; 2n = 6.
»_space;3 bivalents
-> each -> 4 chromatids.
Prophase I: Chromosomes condense Homologous chromosomes -> synapsis -> (pairing) Crossing-over -> genetic material -> non-sister chromatids -> each bivalent Metaphase I: Homologous chromosome pairs -> line up -> equator of cell. Anaphase I: Homologous chromosomes -> separate -> opposite poles of cell -->sister chromatids -> still attached Telophase I: One of original pair -> homologous chromosomes -> each pole of cell Cytokinesis I: Cells divide -> 2 haploid daughter cells ->Each daughter cell -> chromosome -> 2 chromatids
Describe the process of meiosis II
Meiosis II:
Prophase II:
Chromosomes -> attach -> spindle
Metaphase II:
Individual chromosomes -> line up -> equator
Anaphase II:
Sister chromatids -> separate -> opposite poles of cell.
Telophase II:
Each haploid daughter cell -> 1 each type chromosome.
Describe the process of meiosis
Meiosis I:
»_space; 2n = 6.
»_space;3 bivalents
-> each -> 4 chromatids.
Prophase I: Chromosomes condense Homologous chromosomes -> synapsis -> (pairing) Crossing-over -> genetic material -> non-sister chromatids -> each bivalent Metaphase I: Homologous chromosome pairs -> line up -> equator of cell. Anaphase I: Homologous chromosomes -> separate -> opposite poles of cell -->sister chromatids -> still attached Telophase I: One of original pair -> homologous chromosomes -> each pole of cell Cytokinesis I: Cells divide -> 2 haploid daughter cells ->Each daughter cell -> chromosome -> 2 chromatids
Meiosis II:
Prophase II:
Chromosomes -> attach -> spindle
Metaphase II:
Individual chromosomes -> line up -> equator
Anaphase II:
Sister chromatids -> separate -> opposite poles of cell.
Telophase II:
Each haploid daughter cell -> 1 each type chromosome.
State the consequences of meiosis
Independent assortment
Crossing over
Describe independent assortment
Independent assortment:
- Different arrangement of chromosomes -> lined up at equator of cell -> pulled to diff sides of cell -> metaphase
Different combinations -> chromosomes -> gametes
2n different gametes -> generated -> independent assortment
->(n=haploid chromosome no.)
Describe crossing over
- Crossing over -> non-sister chromatids -> diff. homologous chromosomes
New combinations of alleles - Recombinant chromatids -> chromatids which have crossed over during meiosis
- Non-recombinant chromatids -> chromatids which have not crossed over during meiosis
Describe the process of mitosis
• Mitosis: - Prophase: Chromosomes condense Mitotic spindle formed -> (composed -> microtubules) Nuclear envelope -> breaks down Chromosomes attach -> mitotic spindle - Metapahse: Chromsomes line up -> equator of cell Sister chromatids -> attached -> opposite poles -> mitotic spindle - Anaphase: Microtubules contract -> breaks bonds between sister chromatids Sister chromatids pulled -> opposite poles of cell - Telophase: Chromosomes spread out Nuclear envelope reforms - Cytokinesis
What is the centromere?
• Centromere
Assembles kinetochore
—>Attaches to microtubules
What is the telomere?
• Telomere
Stabilise ends of chromosomes
What are recombinant chromatids?
- Recombinant chromatids -> chromatids which have crossed over during meiosis
What are non-recombinant chromatids?
- Non-recombinant chromatids -> chromatids which have not crossed over during meiosis
What are the characteristics of a monohybrid cross?
• Monohybrid crosses: 1 gene loci 2 alleles of gene Eg. Gene -> eye colour -> Blue eyes (b) / brown eyes (B) >>Inheritance -> 1 trait
What are the characteristics of a dihybrid cross?
• Di-hibrid crosses: - 2 different gene loci 2 alleles of each gene. Eg. Gene -> eye colour -> Blue eyes (b) / brown eyes (B) Gene -> eye size -> Small eyes (w) / Wide eyes (W) >>Inheritance -> 2 traits
Phenotypic ratio of F2 generation offspring in monohybrid cross
3:1
Phenotypic ratio of F2 generation offspring in dihybrid cross
9:3:3:1
Offspring Genotypic % ratio -> homozygous parents (RR x rr)
100% heterozygous
-> All -> same genotype (Rr)
% of offspring genotypes & phenotypes -> homozygous parents
(BB x bb)
100% Bb genotype
100% Brown eyes phenotype
% of offspring genotypes & phenotypes -> homozygous parents
(BBpp x bbPP)
100% BbPp genotype
100% Brown eyes & Tanned skin genotype
What would the phenotypic & genotypic results of offspring be for these combinations of genotype. Explain why this is the case.
(BBpp x bbPP)
(BBPP) x (bbpp)
Phenotype:
Both combinations -> 100% BbPp offspring
Both combinations -> heterozygous offspring
Both combinations -> Same physical characteristics
Homozygous mono & di-hybrid crosses will always result in
-> 100% heterozygous offspring
-> 100% offspring of same gentotype & phenotype
Eg. RR x rr–> 100% Rr
Eg. RRbb x rrBB -> 100% RrBb
RRBB x rrbb -> 100% RrBb
Homozygous mono & di-hybrid crosses will always result in
-> 100% heterozygous offspring
-> 100% offspring of same gentotype & phenotype
Eg. RR x rr–> 100% Rr
Eg. RRbb x rrBB -> 100% RrBb
RRBB x rrbb -> 100% RrBb
What is the multiplication rule -> Mendel’s theory of inheritance
> > Rules:
Multiplication rule:
- Random fertilisation
- Independent events -> Probability -> event -> occurs in specific way
Eg. Heterozygote -> Rr
»_space;P(Heterozygote) = P(R) x P(r)
What is the addition rule -> Mendel’s theory of inheritance
Addition rule:
- Random fertilisation
- Mutual event -> Probability -> event -> can occur in more than one way
Eg. Dominant phenotype -> RR / Rr
»_space; P(Dominant phenotype) = P(RR) + P(Rr)
What is Mendel’s 1st law?
• Mendel’s 1st law:
Principle of Segregation:
Alleles of single gene equally segregate -> gametes
What is Mendel’s 2nd law?
• Mendel’s 2nd law:
Principle of independent assortment
Alleles of different genes segregate independently into gametes
Outline the genotypes and phenotypes of offspring from generations 1 & 2 as a result of homozygous monohybrid cross
• Mating -> two homozygous individuals -> one dominant & one recessive
1st generation:
YY & yy
4 x Yy genotypes -> 100% heterozygous Yy
F1 (First filial) offspring -> same genotype (Yy) & phenotype (yellow)
F1 -> first-selfed / self fertilised
2nd generation:
Yy & Yy
1 x YY ; 2 x Yy ; 1 x yy
F2 (Second filial) offspring -> 3 different genotypes -> 1:2:1
-> 2 different phenotypes -> 3:1
»_space;> 3:1 phenotypic ratio -> 2 alleles -> same gene.
Outline the genotypes and phenotypes of offspring from generations 1 & 2 as a result of homozygous dihybrid cross
• Mating -> two homozygous individuals -> one dominant & one recessive
1st generation:
RRyy & rrYY
100% RrYy genotype
100% Round, yellow phenotype
F1 (First filial) offspring -> same genotype (RrYy) & phenotype (Right-handed & yellow)
2nd generation:
RrYy x RrYy
» 9:3:3:1 phenotypic ratio
9 Round yellow / 3 round green / 3 wrinkled yellow / 1 wrinkled green
Outline the genotypes and phenotypes of offspring from generations 1 & 2 as a result of homozygous monohybrid cross & homozygous dihybrid cross
Mono: 1st generation: YY & yy 4 x Yy genotypes -> 100% heterozygous Yy genotype -> 100% yellow phenotype 2nd generation: Yy & Yy -> 2 different phenotypes > 3:1 phenotypic ratio Di: 1st generation: RRyy & rrYY 100% Heterozygous RrYy genotype 100% Round, yellow phenotype 2nd generation: RrYy x RrYy -> 4 phenotypes >> 9:3:3:1 phenotypic ratio