Term
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Definition
| The heterozygote has a unique phenotype that is half way between the two homozygous parents |
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Term
| Example of incomplete dominance |
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Definition
| Snapdragon flower color; RR is red, rr is white and Rr is pink! |
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Term
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Definition
| There is more than one dominant allele and more than one dominant can be expressed at the same time. |
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Term
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Definition
| Sickle cell anemia; both normal hemoglobin and the mutated form can be made at the same time. |
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Term
| Why is a potentially lethal mutation maintained in the population? |
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Definition
| Because it must confer some other benefit. In sickle cell anemia, the homozygous recessive condition may be lethal but the heterozygote has increased protection from another disease, malaria. |
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Term
| What pattern of inheritance is blood types in humans? |
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Definition
| Codominance and multiple alleles |
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Term
| What alleles determine blood types? |
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Definition
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Term
| What are the four human blood types? |
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Definition
| A, B, AB and O. They can be correctly referred to as phenotypes. |
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Term
| Which blood type alleles are dominant and which are recessive? |
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Definition
| A and B are dominant and O is recessive. |
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Term
| What are the possible blood type genotypes in humans? |
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Definition
| A: AA or AO; B: BB or BO: AB and OO |
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Term
| What are the human sex chromosomes? |
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Definition
| X and Y. XX is female and XY is male. |
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Term
| What are sex-linked traits? |
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Definition
| They are traits that are located on the X (and rarely the Y) chromosome. |
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Term
| What are common sex-linked conditions? |
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Definition
| Color blindness, hemophilia, muscular dystrophy |
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Term
| Which sex is more likely to show a sex-linked trait? |
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Definition
| Males since they only have one X chromosome. |
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Term
| What are the three genotypes possible with a sex-linked trait? |
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Definition
| A female could be normal, she could be a carrier or she could have the disorder. For a male, he either has the disorder or he doesn't |
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Term
| What is a carrier of a sex-linked trait? |
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Definition
| A heterozygous female. She has the mutated gene but since she also has a normal gene, she does not show the disorder. |
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Term
| How are sex-linked traits passed from one generation to the next? |
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Definition
| A man who has the disorder will have normal sons and daughters who are carriers. A woman who is a carrier will have sons who may have the disorder and daughters who may be carriers. Sons always get the disorder from their mothers! |
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Term
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Definition
| These are traits that are determined by more than one gene; poly means many. |
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Term
| Examples of polygenic traits |
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Definition
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Term
| How do polygenic traits affect phenotypes? |
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Definition
| Because there are many genes involved, you will see a range in phenotypes |
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Term
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Definition
| Since women have 2 X chromosomes and men have only one, one X chromosome in all female cells is turned off or inactivated. It is a random choice as to which one is inactivated. |
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Term
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Definition
| A condensed, darkly staining body in a female cell; it is the inactivated X chromosome |
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Term
| Why are calico cats always females? |
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Definition
| They are heterozygotes for coat color; they have one allele for black fur on one X chromosome and one allele for orange fur on the other X. It is a random event as to which X is inactivated in different patches of cells |
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Term
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Definition
| When homologous chromosomes or sister chromatids fail to separate during meiosis |
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Term
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Definition
| Nondisjunction of chromosome 21 resulting in 3 copies or trisomy of that chromosome. |
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