6.2 - Patterns of Inheritance Flashcards
How does sexual reproduction lead to variation in genotypes in species?
Meiosis makes gametes with a unique assortment of alleles through crossing-over & independent assortment of chromosomes. Also random fusion of gametes during fertilisation also increases variation in off-spring.
Explain the meaning of the term crossing over.
Swapping of alleles between maternal & paternal homologous chromosomes during prophase I of meiosis. Pairs of homologous sister chromatids exchange portions resulting in a shuffling of alleles.
Other than inheriting characteristics, what else may have an effect on the phenotype of an individual?
The environment.
What is genotype?
The genetic constitution of an organism.
What is phenotype?
Appearance due to alleles. Appearance due to environment.
What is a dominant allele?
A allele that is always shown in the phenotype.
What is a recessive allele?
An allele that is only shown in the phenotype when homozygous.
What is heterozygous?
1 dominate allele, 1 recessive allele.
What is homozygous dominant?
2 dominant alleles.
What is homozygous recessive?
2 recessive alleles.
What is co-dominance?
Where both alleles are dominant, so both are expressed in the phenotype.
What is multiple alleles?
Where there are more than 2 alleles of a particular gene.
How can you prove that the allele for a genetic characteristic is on the X chromosome?
Male offspring are positive for the phenotype even when the father is negative and the mother is negative (heterozygous) because faulty X can only be inherited from mother.
How is a genetic diagram laid out? – to explain flower colour being controlled by a single gene with two codominant alleles.
Parental phenotypes: red flower X white flower
Parental genotypes: CR CR X CW CW
Gametes: CR CW
F1 genotypes: All CRCW
F1 phenotypes: All pink
Gametes: CR, CW, CR, CW
F2 genotypes: CRCR ; CRCW ; CRCW ; CWCW
F2 phenotypes: red ; pink (pink) ; white
Expected F2 phenotypic ratio: 1 :2: 1
Why is a recessive genetic disorder, found on the X chromosome, more likely to shown on male’s phenotypes than female’s?
Males only have one X chromosome so only one allele is needed for it to be expressed. Females need two alleles for it to show in their phenotype.
What is monohybrid inheritance?
The inheritance of a characteristics controlled by a single gene.
What is dihybrid inheritance?
The inheritance of 2 characteristics which are controlled by different genes.
What are the predicted phenotypic ratios for monohybrid, dihybrid and codominant crosses?
Monohybrid cross - 3:1 - dominant : recessive
Dihybrid cross - 9:3:3:1 - dominant both: dominant 1st recessive 2nd: recessive 1st dominant 2nd: recessive both
Codominant - 1:2:1 - homozygous for one allele: heterozygous: homozygous for the other allele
Why are the ratios of offspring genotypes not the same in real life to those calculated in genetic diagrams?
Fertilisation is random.
Why can the allele frequency of a lethal genetic disorder decrease over time?
Affected individuals might struggle to reproduce, therefore the allele will not be passed on to future generations.
What is an autosome?
Any chromosome that is not a sex chromosome (X or Y).
Explain the term linkage.
Two or more genes (loci) on the same chromosome. They do not independently assort during meiosis (metaphase I). Their alleles are passed on to offspring together.