Biology SL chapter 4.3 (Theoretical Genetics)

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Define a genotype, phenotype and locus.
Genotype: allele combination of an organism. Phenotype: characteristics of an organism (determined by combination of genotype and environmental factors). Locus: Particular position on homologus chromosome of a gene.
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Define homozygous and heterozygous and carrier.
Homozygous: having two identical alleles of a gene. Heterozygeous: having two different alleles of a gene. carrier: an individual that has one copy of a recessive allele that causes a genetic disease when homozygous
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Define dominant allele, recessive allele and co-dominant alleles
Dominant: an allele that has the same effect on phenotype whether homozygous or heterozygous. Recessive: an allele that only affects the phenotype when homozygous. Codominant: pairs of alleles that both affect phenotype when present in a heterozygote
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Type A blood
Cannot have B or AB blood. Can have A or O blood. Contains antigen A and Anti-B antibody.
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Type B blood
Cannot have A or AB blood. Can have B or O blood. Contains antigen B, contains anti-A antibody
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Type AB blood
Can have any type of blood. Is the universal recipient. Contains A+B antigens and neither antibody.
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Type O blood
Can only have O blood. Is the universal donor. Has neither A nor B antigens but both antibodies.
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How do sex chromosomes control gender?
Humans have 23 pairs of chromosomes. First 22 pairs are autosomes, each chromosome pair possesses the same genes and structural features. 23rd pair are heterosomes(sex chromosomes) and determine gender. females are XX, males are XY
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Who is responsible for determining the gender?
The Y chromosome contains genes for developing male sex characteristic, therefore the father is always responsible for determining gender. If male sperm contains x chromosome, embryo becomes girl, if Y, it becomes boy.
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Differences between X and Y chromosome
Y chromosome is much shorter than X chromosome and only contains a few genes. X chromosome has genes for haemophilia and colour blindness.
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Define sex linkage
When a gene controlling a characteristic is found on a sex chromosome, and so the trait is associated with predominant gender. Sex linked conditions are usually x-linked.
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Describe inheritance of haemophilia and colour blindness as examples of sex linkage
Both are x-linked recessive conditions. As males only have one allele of this gene, they cannot be carriers. This means they have a higher frequency of being recessive and expressing the trait.
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Explain parental involvement in inheritance of sex-linked conditions.
Males will always inherit an x-linked recessive condition from their mother. Females will only inherit if they receive a recessive allele from both parents. (50% chance if mother is carrier for males, 0% chance if father is unaffected for females)
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Explain that female carriers are heterozygous for x-linked recessive alleles pt1
A person with a recessive allele of a condition that is masked by a normal dominant allele is called a carrier. These people can pass on the trait to the next generation without being affected themselves.
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Explain that female carriers are heterozygous for x-linked recessive alleles pt2
Females can be carriers as they have two X chromosomes while males (XY) cannot be carriers.
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Other cards in this set

Card 2

Front

Define homozygous and heterozygous and carrier.

Back

Homozygous: having two identical alleles of a gene. Heterozygeous: having two different alleles of a gene. carrier: an individual that has one copy of a recessive allele that causes a genetic disease when homozygous

Card 3

Front

Define dominant allele, recessive allele and co-dominant alleles

Back

Preview of the front of card 3

Card 4

Front

Type A blood

Back

Preview of the front of card 4

Card 5

Front

Type B blood

Back

Preview of the front of card 5
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