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Dominant and Recessive Alleles
Dominant and Recessive Alleles
Alleles can come in many forms. They can be either dominant or recessive, and depending on these combinations, an allele pair can be homozygous or heterozygous.
The alleles that help determine a particular trait can be described as dominant or recessive.
What do you think the definition is of dominant?
What do you think the definition is of recessive?
What do you think is the minimum number of dominant alleles that must be present for the trait to be expressed?
What do you think is the minimum number of recessive alleles present for it to be expressed?
When talking about alleles, we use letters to show which allele we mean. For example, dominant brown eyes could be 'B', while the recessive blue eyes can be 'b'. The dominant allele is always upper case and the recessive allele is always lower case. It's always the same letter for the same characteristic.
Look at these different alleles on chromosomes, coding for eye colour. The circles show how this pair of chromosomes would be divided into gametes. Gametes are the sex cells of an organism (eggs and sperm in humans).
An egg (or sperm) will have one chromosome out of each chromosome pair of an organism in them, and fuse with a sperm (or egg) to form new combinations of chromosome pairs in an offspring.
Which gamete has the dominant allele in it?
A) The gamete with the allele 'B'. B) The gamete with the allele 'b'.
Which of these combinations of alleles would produce brown eyes in both cases?
A) BB and Bb B) BB and bb C) Bb and bb
Answer A, B or C.
Select all the options you think are true.
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Combination of alleles in a gene can be described as homozygous or heterozygous. Which of these options do you think are examples of homozygous combinations of alleles. Pick all the options you think are correct.
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Depending on the combination of alleles present in a gene, they can be described as homozygous or heterozygous. A homozygous gene for eye colour could be brown (BB) or blue (bb). A heterozygous gene would be Bb. The capital letter is always first in a heterozygote (not bB).
Which of these is a recessive homozygote?
Can you have a recessive heterozygote?
What word do we use to describe this combination, AA?
If the alleles for tallness are dominant T and recessive t, and we want to express that an organism has the dominant genotype where no recessive genes are present, which would be the correct way to say this?
Give the heterozygote genotype for brown hair using the letter 'B' as alleles.