LGS A-Level OCR Biology - Unit 6 - Patterns of Inheritance Part 1
This deck Species can become reproductively isolated due to seasonal differences in breeding, mechanical incompatibility of reproductive organs, or behavioral differences in courtship.
Genotype
Allele combinations possessed by an organism leading to specific phenotypes
Key Terms
Genotype
Allele combinations possessed by an organism leading to specific phenotypes
Discontinuous variation
Qualitative differences
Clearly distinguishable categories (categorical)
Monogenic inheritance
One/two genes
An allele has ...
Continuous variation
Quantitative differences
Phenotypic diff have a wide range of variation in a pop. (sig affected by environment)
Each allele has a small...
Monogenic inheritance
One gene w/ 2 or more alleles
Monohybrid cross
1 gene, 2 alleles (r and d)
Drawing genetic crosses
Parental genotype
Parental phenotype
Parental gametes
F1 ratio for genotype then phenotypes
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| Term | Definition |
|---|---|
Genotype | Allele combinations possessed by an organism leading to specific phenotypes |
Discontinuous variation | Qualitative differences Clearly distinguishable categories (categorical) Monogenic inheritance One/two genes An allele has a large effect |
Continuous variation | Quantitative differences Phenotypic diff have a wide range of variation in a pop. (sig affected by environment) Each allele has a small effect Polygenic inheritance Large number of diff genes involved |
Monogenic inheritance | One gene w/ 2 or more alleles |
Monohybrid cross | 1 gene, 2 alleles (r and d) |
Drawing genetic crosses | Parental genotype Parental phenotype Parental gametes F1 ratio for genotype then phenotypes |
Codominant inheritance | Involves more than one dominant allele |
Multiple alleles genetic crosses | 1 trait 1 gene >2 alleles |
Example of multiple allele genetic cross | Blood group I A I B I O |
3 ways genetic variation arises from sexual reproduction | IA of homologous chromosomes (M1) Crossing over IA of sister chromatids (M2) |
23rd pair of chromosomes | Only pair that varies in shape and size X - v. large and doesn’t carry genes involved in sexual development Y - V. small, no genetic info, but carries gene that causes formation of male embryos |
Sex linked genes | Characteristics determined by genes carried on X and Y |
Why do sex-linked genes affect males | Y is much smaller so only has one copy of the gene, if recessive allele is found on X but no D allele on Y, male will express the recessive trait (usually condition) Most females will have a D allele present on the 2nd X chromosome so are either normal or a carrier |
Examples of sex-linked conditions | Haemophilia - blood clots v. slowly due to a lack of protein blood clotting factor Red-green colour blindness |
Dihybrid cross | Used to show inheritance of 2 diff characteristics, 2 genes at diff loci, >2 alleles on each |
Expected results of a heterozygous dihybrid cross | 9:3:3:1 |
Why may the actual ratio vary from expected | Fertilisation is random If there is no crossing over, alleles for 2 characteristics will be inherited together if on same chromosome |
Autosome | Any chromosome that is not a sex chromosome |
Autosomal linkage | 2 separate genes are found on the same autosome Represented by diff letters Linked genes are inherited together so offspring usually show same combination as parents (certain gametes are more common) |
W/ no crossing over in autosomal linkage | Gametes stay in parental comb. and offspring show 3:1 phenotypic ratio |