Chapter 17: Inherited Change Flashcards
A characteristic is sex-linked when
the allele that codes for the characteristic is found on one of the sex chromosomes (XX, XY)
Why are most sex-linked genes only found on the X chromosome?
- the Y chromosome is smaller than the X chromosome
- can’t carry as much genetic info
- carries fewer genes
Why are males more likely than females to show recessive phenotypes for genes that are sex-linked?
- most genes coding for sex-linked characteristics are found on the X chromosome because the Y chromosome is smaller/carries fewer genes
- males only have 1 X chromosome
- so they often have only one copy/allele of the gene for the sex-linked characteristic
- so the allele is expressed even if it is recessive
Name a genetic disorder that is caused by faulty alleles found on sex chromosomes
colour blindness, haemophillia
autosomal linkage
- when different genes are found on the same autosome
- inheriting one characteristic means inheriting the other
- inextricably linked *
autosome
chromosomes that are not sex chromosomes
Why are autosomal linked genes inherited together?
They stay together, on the same chromosome during independent segregation in meiosis I
Why is it that the closer the genes are on the chromosome the more linked they are?
- crossing over is less likely to split them up
What is the probability of a homozygous dominant allele (AA) in a population?
p²
What is the probability of heterozygous alleles (Aa or aA) in a population?
2pq
What is the probability of a homozygous recessive allele (aa) in a population?
q²
What does p stand for?
p stands for the probability of the dominant allele in a population?
What does q stand for?
q stands for the probability of a recessive allele being in a population?
Why is this equation true?
p + q = 1.0
- because there are only two alleles
- we know that the probability of one plus the other is going to be 1.0 or 100%
Why is this equation true?
p² + 2pq + q² = 1.0
there are only 4 possible arrangements of the two alleles, it follows that the probability of all four added together must equal 1.0
What is the allelic frequency?
the number of times an allele appears within the gene pool of a population
What is a gene pool?
- all the genetic info of all the individuals in a population
- all the alleles of all the genes of all individuals in a population at a given time
- the total number of alleles
In monohybrid inheritance, the offspring of a pure-breeding dominant parent and a pure-breeding recessive parent are crossed to give the F2 generation. What is the theoretical ratio of this F2 generation and what is the genotype of the F1 generation?
The ratio is 3:1
3 offspring showing the dominant characteristic (AA,Aa)
1 offspring showing the recessive characteristic (aa)
the F1 generation are all heterozygous and show the dominant trait (Aa)
when they are crossed with each other it produces the 3:1 ratio
What is monohybrid inheritance?
monohybrid inheritance is the inheritance of a single gene/characteristic
What is it called when the heterozygous plants of an F1 generation are crossed with one another.
F1 intercross
Why is it that the actual results of genetic crosses are rarely the same as the predicted results?
the fusion of gamete is random/determined by chance
What is a ratio?
a ratio is a measure of the relative size of two or more cases that is expressed as a proportion
What is the name given to the situation when a gene has more than 2 allelic forms? (human ABO blood group)
multiple alleles
What is it called when two alleles both contribute to/are expressed in an organism’s phenotype?
codominance
What is dihybrid inheritance?
dihybrid inheritance is the inheritance of 2 or more different genes that are located on different chromosomes
Give an example of dihybrid inheritance.
seed shape and seed colour in pea plants 4 different arrangements of gametes: GR, Gr, gR, gr G = green g = yellow R = round seed r = wrinkled seed
