Chapter 8: Genetics: Mendel & Inheritance Flashcards
Maternal and Paternal chromosome pair
Gene
Human have
23 pairs of chromosomes = (46 individual chromosomes) and two copies of each gene
Maternal gamete: egg + Paternal gamete: sperm
Gametes unite during fertilization
Each human gamete has just
One copy of each chromosome and, thus, one copy of each gene
Child inherit one set of
Chromosomes from each parent and thus two copies of each gene
Heredity (inheritance)
Passing characteristics parents to offspring by sexual reproduction
Variation in traits (characteristics) via alleles
Different versions of a gene
Some trait are controlled by
Just one gene (single-gene traits) and most are multifactorial and eye colors
Gregor Mendel
Discovered rules of inheritance decades before modern understanding of genetics
Working with pea plants, realized characters had
Particular forms (traits) (white/purple, tall/short)
Looking for heritable traits:
Traits passed from parents to offspring
True breeding traits (a plant that always produces)
Offspring like it
Generally, crossed parental generation (P) to produce
1st filial generation (F1), which then self-pollinate to 2nd filial generation (F2)
F1 plants exhibiting one trait sometimes produced
Offspring (F2) with another trait
F1 plants exhibiting one trait sometimes produced
Offspring (F2) with another trait
Dominant (capital letters) and recessive (lower case letters) version of traits
Dominant will express over recessive and trait along with it
Accepting particulate theory: If no blending occurs, inheritance must be through
Discrete units (particles), must get one from each parent and can pass on either to offspring
Gene
Unit of inheritance, a sequence of DNA found on a chromosome at the locus (loci)
Allele
Different forms of a gene
Genome
All of the genes in an individual
Allele: If you carry two copies of a gene (2 allele)
1) You must be diploid (1 copy = haploid)
2) You could carry different copies (heterozygous)
3) You could carry the same copy (homozygous) and they could be dominant or recessive
The genes you carry =
Genotype
The traits you exhibit =
Phenotype
Mendel law: First law:
The law of segregation
Gametes will always get
1 of the 2 copies (alleles) that the parent has (via meisois)
In a cross between true breeding parents:
AA x aa
All offspring must have
Genotype Aa
One character breeding =
Monohybrid cross
Can use a Punnett square to
Estimate offspring genotypes and phenotypes
A Punnett square is
Showing the probability (chance) of getting a particular genotype
1) Probability: 1 = 100%
2) Probability: 0 = 0%
3) Probability: 0.5 = 50%
Should have 50% (0.5) chance of inheriting either allele of parent for
All genes
Test crosses can
Determine genotype of an unknown organism (heterozygous or homozygous)
Cross unknown (brown) with known (true-breeding)
Recessive white
If unknown is homozygous, all progeny will be like
Unknown (brown)
If unknown is heterozygous, only half of progeny will be like
Unknown (brown/white)
Mendel’ laws: Second laws
The law of independent assortment
Alleles are inherited
Independently of other alleles
In a test cross of parents:
AaBb x AaBb
Gametes are equally likely to get
Aa or AB (A and B are not influenced by each other)
Two character breeding
Dihybrid cross
Independent assortment: Generally true
Make recombinant phenotypes (some of mom and some of dad)
Independent assortment happens
If genes are unlinked
In some cases, genes that are
Physically close together (their loci are near each other), tend to get inherited together (linked)
Chromosome are independently assorted, but
Genes might not be
When trait is recessive, can have
Carriers (non-affected individuals who can pass on the allele)
One good copy can mask
The presence of a bad copy
Two bad copies expresses
The trait
Sex-linked traits
Trait carried on sex chromosomes
Particular problem: If the problem is recessive, males are more likely to be
Affected (hemophilia and colorblindless)
Sex-linked traits: Colorblindness
1) Recessive allele carried on the X-chromosome is non-functional
2) Relatively rare, since only need 1 functional copy to distinguish colors
3) Far more common in males than females
4) For a female to be colorblined, must inherit 2 colorblind alleles (thus dad must be colorblind and mon must be a carrier or colorblind)
Dominance issues: Not all traits have
Simple expression
Dominance issues: Incomplete dominance
Provides a middle (intermediate) phenotype
Codominance
Equal expression of different alleles
Multiple alleles
1) Although individuals only carry 2 alleles, there may be more alleles available
2) Blood type alleles for O, A and B
Polygeny/Pleiotropy: Unlike single-gene traits, many traits are influenced by
Multiple genes (polygenic)
Reverse of polygeny =
Pleiotropy: one gene influencing multiple traits
Nature vs Nurture: Environment can have a large role in
Translation between genotype and phenotype
