Human Inheritance
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Transcript of Human Inheritance
Human InheritanceHuman Inheritance
Key Concepts1.What are some patterns of inheritance in humans?2.What are the functions of the sex chromosomes?3.What is the relationship between genes and the environment?
Patterns of Human InheritancePatterns of Human InheritanceHuman traits are controlled by:◦ single genes with two alleles◦others by single genes with multiple alleles. ◦Still other traits are controlled by many genes
that act together
Single Gene with Two AllelesSingle Gene with Two AllelesHave 1 dominant and 1 recessive alleleHave 2 distinctly different phenotypesEx. Widow’s Peak◦Smile dimples – Draw a Punnett Square that
shows a cross between two heterozygotes for smile dimples
Single Genes with Multiple AllelesSingle Genes with Multiple Alleles
Some traits have more than 2 alleles although a person can have only 2 of those alleles because chromosomes exist in pairs. Each chromosome in a pair carries only 1 allele for each gene
Ex. Human blood type – 3 alleles A, B, O A and B are codominant O is recessive
Traits Controlled by Many GenesTraits Controlled by Many GenesProduce a large variety of phenotypesGenes act together as a group to
produce a single traitEx. Height – at least 4 genes◦Skin color – at least 3 genesQuestion: In our face trait lab most of the
children had dark colored skin. What was the assumption about the parents that caused this result?
The Sex ChromosomesThe Sex ChromosomesOne of the 23 pairs of chromosomes that
carries the genes that determine whether a person is male or female
Also carries genes that determine other traits
Girl or Boy?Girl or Boy?The only chromosome
pair that does not always match
Girl – two sex chromosomes match (X,X)
Boy –don’t match, one is an X other is a Y◦The Y chromosome is
smaller than the X
Sex Chromosomes and FertilizationSex Chromosomes and Fertilization
Egg cells all carry an X chromosomeSperm cells carry either an X or a YWhen a sperm cell with an X
chromosome fertilizes an egg cell, the egg has 2 X’s = girl
When a sperm cell with a Y chromosome fertilizes an egg cell, the egg has an X and a Y = boy
Sex-linked GenesSex-linked Genes
Genes for some human traits are carried on the sex chromosomes
Traits controlled by sex-linked genes are called sex-linked traits
EX. Red-green colorblindnessMost of the genes on the X chromosome
are not on the Y chromosomeAn allele on the X may not have a match
on the Y
Sex-Linked GenesSex-Linked Genes
Sex-linked genes can have dominant and recessive alleles
In females a dominant allele on one x will mask a recessive on the other X
In males, there is no matching allele on the Y to mask a recessive allele on the X
Any trait on the X chromosome in males (even a recessive trait) will produce the trait in a male who inherits it.
Inheritance of ColorblindnessInheritance of ColorblindnessColorblindness is a trait controlled by a
recessive allele on the X chromosomeMany more males have colorblindness
than femalesFemales can be carriers. They have one
dominant trait for normal color vision and one recessive trait for colorblindness. They have normal color vision
Inheritance of ColorblindnessInheritance of ColorblindnessIf the mother passes on the X
chromosome to a son, he will be colorblind
If she passes it onto a daughter, she will also have an X chromosome from her father. If her father has normal color vision, then she will inherit the dominant allele for normal color vision from him and she will have normal color vision
Inheritance of ColorblindnessInheritance of Colorblindness
XCY
XC
Xc
MotherXCXc
Father XCY
XCXC XCY
XCXc XcY
The Effect of EnvironmentThe Effect of EnvironmentMany of a person’s characteristics are
determined by an interaction between genes and the environment
Several genes work together to determine height
Environment affects height – a poor diet can prevent a person from reaching their potential
Environmental factors can also affect human skills – Ex. Playing a musical instrument – need instruction to play well