Topic 7A - Genetics Flashcards
Define these key words:
- Gene
- Allele
- Genotype
- Phenotype
- Gene = a sequence of DNA bases that codes for a particular protein.
- Allele = a different version of a gene
- Genotype =the combination of alleles (Bb)
- Phenotype =the organisms characteristics.
Define these key words:
- Dominant
- Recessive
- Codominant
- Locus
- Homozygote
- Heterozygous
- Carrier
- Dominant: allele whose characteristic appears in phenotype even if there’s only copy.
- Recessive: allele that needs to 2 copies to appear in phenotype
- Codominant: alleles that are both expressed in phenotype
- Locus: the fixed position of a gene on a chromosome. Alleles of a gene are found at the same locus on each chromosome in homologous pair.
- Homozygote: 2 copies of same allele
- Heterozygote: 2 copies of different allele.
- Carrier: A person carrying an allele which is not expressed in their phenotype but can be passed on to offspring
practise drawing monohybrid crosses
page 168
practise drawing Punnett square diagrams
page 169
How many alleles are there for each gene in a diploid organism?
2
How many alleles are there for each gene in gametes?
1
Define monohybrid inheritance
The inheritance of a characteristic controlled by a single gene
practise drawing codominance genetic diagrams
page 169
practise drawing blood group genetic diagrams
page 169
practise drawing dihybrid crosses
page 170
Define phenotypic ratio
The ratio of different phenotypes in offspring
What do dihybrid crosses show you?
They show you how 2 different genes are inherited at the same time
What are the main differences between the Y chromosome and the X chromosome?
The Y chromosome is smaller than the X chromosomes and carries fewer genes
Why are males more likely to inherit a sex-linked disorder such as colour blindness?
- As the X chromosome is bigger, it carries more genes and therefore, determines more characteristics.
- Some genes that are carried by the X chromosome have faulty alleles such as the one for colour blindness.
- As females are XX, they need two copies of the faulty allele to show the characteristic, whilst males only need 1 as the Y chromosome doesn’t carry the faulty allele.
Practise drawing genetic diagrams for sex-linked disease
Page 171
Define:
- Autosome
2. Autosomal genes
- Autosome = Any chromosome that isn’t a sex chromosome
2. Autosomal genes = the genes found on the autosome
What is important about genes found on the same autosome?
Genes on same autosome are said to be linked as it’s assumed they stay together during independent segregation of chromosomes in meiosis I, and their alleles will be passed on to offspring together. Only time this wont happen is if crossing over splits them up first
- The closer together 2 genes are on autosome, the more closely they are said to be linked. This is because crossing over is less likely to split them up
How can autosomally linked genes affect the phenotypic ratio?
The result would most likely be that which you’d expect in a monohybrid cross, not a dihybrid cross, as the 2 autosomally-linked alleles are inherited together. This means a higher proportion of the offspring will have their parents genotype and phenotype.**
practise drawing and explaining genetic diagrams that show autosomal linkage
page 172
Does only one single gene control a characteristic?
No, many different genes can interact to control the same characteristic
What is epistasis?
Epistasis is when an allele from 1 gene blocks the expression of the alleles of other genes (when they interact to control a phenotype)
What do epistatic genes affect (in terms of expected phenotype ratios)?
Crosses involving epistatic genes don’t result in the expected phenotypic ratios as there is no chance a characteristic will be expressed if it is blocked by an epistatic gene.
Practise questions on how to predict phenotypes of epistatic genes
page 173
Practise questions on chi-squared
pages 174-175
