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CSULB BIO 212 section 12.4
Chapter 12.4 Inheritance, Genes, and Chromosomes
13
Biology
Undergraduate 1
04/19/2011

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Term
Linkage Group
Definition
formed from all loci on a chromosome
Term
Morgan's Experiment with fruit flies
Definition
Hypothesis: alleles for different characteristics always assort independently

Method:Female, wild type, gray body, normal winds mate with male, black body,vestigial wings.

Results: Actual results were inconsistent with Mendel's 2nd law of segregation.

Conclusion:hypothesis rejected. The 2 genes don't assort independently but are linked on the same chromosome
Term
Review: What's Mendel's 2nd law of segregation?
Definition
Alleles of different genes assort independently of one another during gamete formation.
Term
Linked Genes
Definition
Genes that don't assort completely independently (50%) are linked

These genes travel together on a chromosome
Term
Absolute linkage
Definition
is rare

genes at different loci on the same chromosome do sometimes separate

Genes may recombine during prophase I of meiosis by crossing over.

Chromosomes exchange corresponding segments. The exchange involves 2 chromatids in tetrad

Both chromatids become recombinant.
Term
Recombinant frequencies
Definition
= # of recombinant offspring/ total # of offspring

recombinant offspring phenotypes appear in recombinant frequencies

is greater for loci that are farther apart

Can be used to make genetic maps
Term
Genetic maps
Definition
shows arrangement of genes along a chromosome
Term
Map unit
Definition
distance between genes

=recombinant frequency of 0.01

Also called centimorgan (cM)
Term
Sex-linked inheritance
Definition
= a character is governed by loci on the sex chromosomes

In animals, sex determined by 1 or a pair of sex chromosomes

sex of offspring depends on which chromosome fertilizes the egg.

Genes on sex chromosomes don't follow Mendelian patterns.

Y chromosome carries few genes
X chromosome carries many
Term
Autosomes
Definition
both sexes have 2 copies of all other chromosomes
Term
Hemizygous
Definition
Males have only one copy of these genes
Term
X-linked recessive phenotypes
Definition
Appear much more often in males than females.

Carriers

Mutant phenotype can skip a generation if it passes from a male to his daughter.
Term
Carriers
Definition
Daughters who are heterozygous
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