chapter 10.5 Flashcards
Genes on the same chromosome maybe
inherited together
alleles of a gene are from homologous pairs so are packaged in
different gametes
How do a few chromosome control so many genes
Each chromosome carries many genes
LINKED genes
Are carried on the same chromosome, they are inherited together .
They do not assort independently during meiosis
comparisons between genes and chromosomes
- they both come in pairs
2.alles of a gene are packaged into separate gametes
. so are members of homlogous pairs - Both are inherited in random combinations
The affect of gene linkage on dihybrid cross versus no gene linkage
When Genes are not lined on the same chromosome they assort independently
The gametes then represent all possible allele combinations, and the cross yields the expected phenotypic ratio.
When genes are linked on the same chromosome, only two allele combinations are expected in the gametes, and the number of phono types are reduced
LINKAGE GROUPS
collection of genes that tend to be inherited together
Why do offsprings sometimes have trait combinations not seen in either parent
CROSSING OVER : an exchange of genetic material between homologous chromosomes during prophase I
. After crossing over no two chromatids in a homologous pair of chromosome are identical
What is the purpose and end result of CROSSING OVER
no 2 chromatids in a homologous pair of chromosomes are identical
2 options of chromatids of that a gamete could inherit after crossing over
- Parent chromatid
2. Recombinant chromatid
PARENTAL CHROMATID
retains the allele combination from each parent.
RECOMBINANT CHROMATID
the result of two genes crossing over; has a mixture of maternal and paternal genes
LINKAGE MAPS
diagrams of gene order and spacing on chromosomes ( vertically).
It shows the likelihood of a gene allele being seperated from another based on theirs pacing
What concept are linkage maps based on
the farther apart 2 alleles are on the same chromosome, the more likely crossing over is to separate them- simply because more separates the genes
How are linkage maps used
By determining the the percentage of recombinant offsprings, one can infer how far apart the genes are on the chromosome
Why are the percentage of recumbent offsprings
Crossing over frequently sperates alleles on opposite ends of the same chromosomes. In contrast an crossover would rarely separate alleles lying very close together and the percentage of recombinant offsprings would be small
GENETIC MARKER
a DNA sequence with a known physical location on a chromosome. they help link an inherited disease with the responsible gene
. How do patterns of inheritance differ for unlinked versus linked pairs of genes?
When pairs of genes are linked, they are carried on the same chromosome and are inherited together. Crossing over complicates the inheritance of linked genes; sometimes allele combinations differ from either parent. The inheritance pattern of non-linked genes is more predictable since it is not affected by crossing over. The inheritance of non-linked genes can be visualized using a Punnett Square.
What is the difference between recombinant and parental chromatids, and how do they arise?
Recombinant chromatids are chromosomes that have a mixture of maternal and paternal alleles ( crossing over occurred between two non-sister chromatid) instead of alleles from just a single parent. In contrast, parental chromatids carry the same combinations of alleles that were inherited from the parents. Crossing over has not altered them.
How do biologists use crossover frequencies to map genes on chromosomes
The farther apart genes are on a chromosome, the more frequently they will cross over. By comparison, genes that are close together on a chromosome are less likely to be separated. Analysis of how often the traits appear together helps to establish linkage maps, which show the relative positions of genes on chromosomes.
Another term for crossing over is
RECOMBINATION
