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Flashcards in Inheritance Deck (48)
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1

homozygote

gene with two identical alleles (PP, pp)

2

heterozygote

gene with two different alleles ( one of them is dominant -> visible and the other recessive (Pp)

3

First Mendelian Law :
Law of Segregation

The two alleles for the heritable characteristic segregate during gamete formation (meiosis) and end up in different gametes

-> If two hetereozygote individuals are crossed with one another ( F1 genertaion)

4

allele

alternative form of gene that accounts for variations in inherited characters
example
gene : hair colour
allele1 blond; allele2 brown

5

Punnet Square

predicts allele composition

6

true-breeding

p generation are both homozygote (PP and pp)

7

ratio in f1 and f2 generation after true breeding

f1 : Pp Pp Pp Pp (4:0)
f2. PP Pp Pp pp (3:1)

8

Law of Independent Assortment

- Each pair of alleles segregats independently of each other pair during gamete formation
- each gene has an independent biologically effect

9

Law of Dominance

recessive allele will be always masked by dominant allele

10

Mendelian Disease -> lethal recessives

Lethal recessives - recessive allele that causes death of an organism that carries it

- an individual carrying a aingle recessive deleterious allele will be healthy and can easily pass the deleterious allele into next generation as long as population is large as then -> rarely expressed

REASON TO AVOID INBREEDING

11

co-dominant genes

fully express the phenotype of both of homozygous parents

12

Complete dominance

dominant allele completely masks the recessive one
- one copy of the dominant allele is enough to produce some enzyme

13

Incomplete dominance

heterozygous phenotype intermediate between the two homozygous phenotypes

14

Co-dominance

two allels each affect the phenotype in seperate, distinguishable way , both phenotypes are fully expressed
eg blood group

15

Pleiotropy

one gene affects multiple phenotypic characteristics

-> causes multiple disesase eg albinism

16

Epistasis

the phenotypic expression of a gene at one locus alters the that of a gene at another locus
-> the gene that affects another is 'epistatic' to that other gene
-> modyfies 9:3:3:1 ratio

17

Quantitative characters

classification is impossible as they vary along a continuum ( eg skin colour)

18

Polygenic Inheritance

additive effect of multiple genes on a single phenotypic character
Eg AABBCC -> darkest
AaBbCc -> middle
aabbcc-> lightest ( majority of the population is in the middle)

19

Norm of reaction for a genotype

genotype is generally not associated with one definite phenotype but rather with a range of phenotypic possibilities ( broadest for polygenic characteristics)

20

Multifactorial characters

refers to both genetic and environmental factors ; collectively influence phenotype

21

Linkage

when two genes lie on the same chromosome
closer together -> greater linkage

22

Variation

- provides raw material for natural selection
- interplay between environment and genotype will determine which genetic combinations persist over time
- if new arised traits better suit for a given environment , organisms possessing those will thrive and leave more offspring -> next generation: generation again shuffled

23

Hardy Weinberg - conditions

1 no mutation in gene pool
2 random mating
3 extremely large population size
4 no gene flow ( from and to other populations) -> no migration
5 no selection

24

Hardy Weinberg Principle

the frequencies of alleles and genotypes in a population will remain constant from generation to generation provided that only Mendelian segregation adn recombination of alleles are at work -> equilibrium

25

HW - theorem

p = frequency of one allele q= frequency of the other allele
p+q=1
p*2+2pq+q*2=1

26

HW and natural selection

NS occurs when the frquencies change a

27

Equilibrium

- if expected frequencies are same as actual frequencies
- some genes can be in equilibrium while other at same time arent

28

Genetic Drift

- the smaller a population the more frequencies will fluctuate
- new mutations can fluctuate all the way till point where everyone has it -> muations becomes fixed
- the number of new mutation arising is greater the greater the population

29

Neutral Theory of Molecular Evolution

amount of divergence between the dna sequences of two populations reflects their time since their common ancestor -> molecular clock

- accounts for much of the functionless molecular change not phenotype

30

Heritability (h2)

proportion of the observed phenotypic variation between individuals that can be accounted for by genetic variation
-> soil example demonstrates this