U2T5 - Inheritance Flashcards
Genes + Patterns of Inheritance
What does it mean if a gene has 2 alleles?
There are 3 possible combinations/genotypes that the organism may have. Dom/recessive homozygosity or heterozygosity.
What did Mendel base his first law on?
Observations on outcome of monohybrid crosses from pea plants.
Why is there only 1 gene for a characteristic in a gamete?
Meiosis 1 is reduction division + separates homologous chromosomes. Since each chromosome carries 1 gene at same locus in each, only 1 gene in each gamete.
What is the ratio for:
2 hetero
1 homo + 1 hetero
3: 1
1: 1
Why do 2 genes act independently of each other?
When pairs of homologous chromosomes arrange themselves on spindle equator during metaphase 1 of meiosis, they do so randomly. This random distribution + independent assortment produces new genetic combinations.
What is an example of multiple alleles?
Human ABO blood groups. 3 possible alleles (A,B,O) represented normally by IA, IB, IO. A + B are codominant so in genotype IAIB, both expressed. Both dominant to O which is recessive so 4 poss blood groups.
What are the 4 human blood groups and their possible genotypes?
A (IAIA, IAIO), B (IBIB, IBIO), AB (IAIB), O (IOIO)
What are the male and female sex chromosomes?
M = XY - Heterogametic F = XX - Homogametic
Describe sex chromosome inheritance.
Homologous pairs of chromosomes come from each parent, half from mum + half from dad. All gametes contain 1 of 2 sec chromosomes which pair up at fertilisation. Inherit sex chromosome from dad, determines sex.
What causes Down’s Syndrome?
Three copies of chromosome 21.
Discuss how cats inherit coat colour.
Locus on x chromosome. Females have 2 alleles for coat colour + males only 1. Xo produces orange, Xb produces black. Codominant so both expressed in hetero, creates tortoiseshell cats (XoXb)
Describe an example of polygenic inheritance.
Inheritance of seed colour in wheat. Determined by 3 genes on diff chromosomes. Each has 2 alleles. Dark red have genotype R1R1R2 R2R3R3. White is r1r1r2 r2r3r3. Colour determined by num of R alleles, not r alleles.
Why are sex chromosomes usually carried on the X chromosome?
It’s larger so can carry many genes not present on Y chromosome, but y chromosome may carry some male gender characteristics.
What does it mean if the phenotypic ratio is 1:2:1?
Codominance.
Is it possible for parents of blood group B and A to produce any of 4 blood groups, especially O?
Yes as O can be produced from hetero A + B blood groups.