inheritance Flashcards
what is genotype?
the genetic constitution of an organism.
what is the phenotype?
expression of this genetic constitution and its interaction with the environment.
what is a recessive allele?
only expressed in the phenotype when 2 copies are present
(homozygous)
what is a dominant allele?
always expressed in the phenotype when present.
what is monohybrid inheritance?
inheritance of a single gene which determines a single characteristic.
Two long winged flies mated and produced 70 long winged flies and 23 vestigal winged flies (wings reduced to a stump). What was the genotype of the parents, + draw a genetic cross
The vestigial winged flies must have got their alleles (for vestigial wing) from their parents. As it did not show in the parents but was present, then the allele must be recessive (and long wing dominant). The vestigial wing flies must have the genotype ww, therefore must have got a w allele from each parent. Both parents must be Ww.
why do genetic crosses rarely have predicted results?
- Fertilisation of gametes is random
- May be a small sample
- Some alleles may give a selective advantage / selective disadvantage/ be a lethal allele
what are co-dominant alleles?
both are expressed in the phenotype
give a cross for flower colour in snapdragons (C is used for colour and R for red allele and W for white allele- they are co-dominant). The parent genotypes are cRcR + cWcW.
what is sex linkage?
a gene carried on the X chromosome.
why are males more likely to express recessive phenotypes?
As males only have 1 X chromosome, males only need one copy of the recessive allele for it to be expressed in the
phenotype whereas females need 2 copies of the recessive allele.
If these recessive genes are alleles for a disease, the male will suffer. If the female is heterozygous, she will not suffer
from the disease but will be a carrier for that disease.
They show a mother to son and father to daughter inheritance pattern and often skip a generation.
draw a cross where the mother is a carrier for haemophilia (xHxh) and the father is a non-sufferer (xH Y)
what is dihybrid inheritance?
2 different characteristics, determined by 2 different genes on different chromosomes are inherited.
how did gregor mendel investigate dihybrid inheritance + draw a cross for this
Gregor Mendel investigated 2 characteristics of pea plants at the same time:
* Seed shape – round shape (R) is dominant to wrinkled (r)
* Seed colour – yellow (G) is dominant to green (g)
what is autosome linked inheritance?
inheritance of 2 or more genes carried on the same autosome
give a cross between dragonflies, both with grey body and normal wings (GgNn)
g=black, n=vestigial
In bean plants, the genes for length and type of leaf are on the same homologous pair of chromosomes. Results for the cross of 2 heterozygous plants for length + colour of leaves are shown.
Explain the results of the table.
The genes are linked as they are on the same chromosome.
The genes for long and normal leaves are linked and the genes for short and mottled leaves are linked so that is why there are mainly LN gametes, producing long normal leaves, and ln gametes, producing short mottled leaves.
However crossing over occurs to produce Ln gametes, giving long mottled, and lN gametes, giving short normal leaves, but there are fewer of these produced.
