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Chapter 8 -- Part 3: Heredity
Only two kinds of progeny phenotypes are produced and they would be produced in equal numbers without crossing over.
The table has the largest numbers, and .
The smaller numbers represent the offspring that are produced as a result of crossing over.
The total number of offspring produced is 166.
The total number of offspring is 77 + 88 + 683, or 1,500.
All the genes on the X chromosomes are expressed by males regardless of whether they are dominant or not.
In order for a female to express a trait, she must have two X chromosomes and two alleles for the same gene.
Because females have two X chromosomes, they can inherit a trait on one of them and only need one copy of a dominant allele to express it.
Continuous variation in a population is caused by a trait that is produced by the expression of many interacting genes.
Many genotypic and phenotypic combinations can be produced by multiple alleles of a single gene.
During meiosis I, the chromosomes align on the metaphase plate.
Each homologue migrates to a different pole and becomes a different gamete.
The migration to separate poles is random because either of the chromosomes can migrate to either pole.
There are different pairs of chromosomes.
The law of independent assortment states that genes that are on different chromosomes migrate independently of genes on other chromosomes.
Two genes are on the same chromosomes.
Unless crossing over occurs, they migrate to either pole if they are on the same chromosomes.
They violate the law of independent assortment by being a single gene in a mono hybrid cross.
The genotypic and phenotypic ratios are expected from a typical mono hybrid cross.
There is crossing over between genes.
As the distance between the genes increases, the crossing over increases.
Sex-linkage occurs when a gene is located on one of the sex chromosomes.
In humans, there is an allele on the X chromosomes that causes hemophilia.
Females have two copies of the gene on their X chromosomes.
They are a type of bleeding disorders if they receive two all genes.
If they inherit one of the two normal all genes, they will have normal clotting abilities but will be carriers of the disease.
They will have normal clotting if they receive the normal allele.
Sex-linked diseases are more common in males than in females because they only need one copy of the allele to express the trait.
Down syndrome is caused by the nondisjunction of the two number 21 chromosomes.
The law of segregation states that the homologous pair does not separate and move to opposite poles, but rather they end up at the same pole and gamete.
There are two kinds of gametes, one with two copies and one without.
Only two copies of the chromosomes are viable.
There are three copies of chromosomes 21 in the zygote formed between this gamete and a normal gamete.
This results in a gamete with either two sex chromosomes or no sex chromosomes.
If a gamete with no sex chromosomes is combined with a normal gamete, the result will be a single X chromosomes and Turner syndrome.
Turner syndrome individuals are female and have physical defects.
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