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Chapter 25
Genetics
23
Biology
9th Grade
04/25/2011

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Term
What is genetics?
Definition
The study of heredity or inheritance
Term
Gregor Mendel
Definition
Gregor Mendel is known as the “Father of Genetics”
Monk who experimented with peas and discovered the basic principles of genetics
Term
ALLELES
Definition
Different versions of the same gene
Term
GENES
Definition
Inheritance is determined by genes passed on from one generation to the next.
Term
dominant allele
Definition
characteristic that shows if one dominant allele is present
masks other alleles
Term
recessive allele
Definition
no noticeable effect
only shows if all the alleles are recessive.
Term
law of dominance
Definition
Dominant alleles mask the recessive alleles unless all the alleles are recessive.
Term
phenotype
Definition
Physical description of an organism’s trait
Term
genotype
Definition
Description of an organism’s genetic make-up
Term
Punnett Squares
Definition
Shows possible allele combinations from a genetic cross.
Gametes from parents are shown along the top and left side of square.
Possible offspring allele combinations are shown in the boxes making up the square
Term
Homozygous Dominant
Definition
Two dominant alleles (two capital letters)
E.g. true breeding purple flowers (PP)
Term
Homozygous Recessive
Definition
Two recessive alleles (two lowercase letters)
E.g. true breeding white flowers (pp)
Term
Heterozygous
Definition
One dominant allele and one recessive allele (one capital, one lowercase letter)
E.g. hybrid purple flowers (Pp)
Term
Monohybrid Cross
Definition
Cross involving one pair of contrasting traits
Term
Incomplete Dominance
Definition
One allele is partially dominant over the other.
Sometimes called blending inheritance
The heterozygous phenotype is a combination of the dominant & recessive
Term
Codominance
Definition
Neither allele is dominant over the other
Both alleles can be expressed
E.g. red cow x white cow = roan cow
Roan is a cow that have red and white coats
Term
Multiple Alleles
Definition
In some traits more than two alleles can exist in a population of a species, but a single individual can only possess two alleles.
E.g. Human blood has 3 alleles – A, B, & O
Term
Sex-linked traits
Definition
Sex chromosomes have other genes on them, too
especially the X chromosome
hemophilia in humans
blood doesn’t clot
Duchenne muscular dystrophy in humans
loss of muscle control
red-green color blindness
see green & red as shades of grey
Term
Polygenic Inheritance
Definition
Aka Multiple-gene inheritance
Two or more independent genes affect one characteristic
Usually seen in traits that vary between two extremes
Human Examples:
skin color, height, weight, eye color, intelligence
Term
Cross-pollinate
Definition
When two or more flowers pollinate each other.
Term
Self-pollinate
Definition
when a flower pollinates iteself
Term
Segregation
Definition
Alleles segregate from each other during meiosis so each gamete only carries one allele for each gene.
Term
Independent Assortment
Definition
Genes of different traits can segregate independently during the formation of gametes
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