Download Heredity

Ch. 8 class notes
HEREDITY
• Heredity -
Ch. 8 class notes
HEREDITY
• Heredity - The passing of characters
(traits) from parents to offspring
Ch. 8 class notes
HEREDITY
• Heredity - The passing of characters
(traits) from parents to offspring
• Genetics -
Ch. 8 class notes
HEREDITY
• Heredity - The passing of characters
(traits) from parents to offspring
• Genetics - the study of heredity
• Gregor Mendel (1822-1884)
– Determined mechanism of inheritance –
parents transmit discrete inheritable factors
(genes) that remain as separate factors from
one generation to the next. This disproved
the “blending” hypothesis of the time.
– Worked with the garden pea plant to study
heredity
• Genes –
• Genes – sequence of triplets on DNA
• Genes – sequence of triplets on DNA
• Humans have about –
• Genes – sequence of triplets on DNA
• Humans have about – 23,000 genes
• Genes – sequence of triplets on DNA
• Humans have about – 23,000 genes
• Each chromosome contains
• Genes – sequence of triplets on DNA
• Humans have about – 23,000 genes
• Each chromosome contains many genes
•
•
•
•
Genes – sequence of triplets on DNA
Humans have about – 23,000 genes
Each chromosome contains many genes
Like the chromosomes they are part of,
•
•
•
•
Genes – sequence of triplets on DNA
Humans have about – 23,000 genes
Each chromosome contains many genes
Like the chromosomes they are part of,
genes occur in pairs of two.
•
•
•
•
Genes – sequence of triplets on DNA
Humans have about – 23,000 genes
Each chromosome contains many genes
Like the chromosomes they are part of,
genes occur in pairs of two.
– Alleles -
•
•
•
•
Genes – sequence of triplets on DNA
Humans have about – 23,000 genes
Each chromosome contains many genes
Like the chromosomes they are part of,
genes occur in pairs of two.
– Alleles - alternate forms of a gene
•
•
•
•
Genes – sequence of triplets on DNA
Humans have about – 23,000 genes
Each chromosome contains many genes
Like the chromosomes they are part of,
genes occur in pairs of two.
– Alleles - alternate forms of a gene
• Each pair of alleles controls
•
•
•
•
Genes – sequence of triplets on DNA
Humans have about – 23,000 genes
Each chromosome contains many genes
Like the chromosomes they are part of,
genes occur in pairs of two.
– Alleles - alternate forms of a gene
• Each pair of alleles controls one trait
• Body cells contain
• Body cells contain both alleles of a pair.
• Body cells contain both alleles of a pair.
• Gametes contain only
• Body cells contain both alleles of a pair.
• Gametes contain only one allele of a pair.
• Body cells contain both alleles of a pair.
• Gametes contain only one allele of a pair.
• Traits are passed on when gametes
unite in fertilization. For each trait, the
offspring gets one allele of the pair from
the mom and one allele of the pair from
the dad.
• Types of Alleles
• Types of Alleles
– Dominant alleles –
• Types of Alleles
– Dominant alleles – expressed in the
appearance of the trait.
• Types of Alleles
– Dominant alleles – expressed in the
appearance of the trait.
Mendel’s example:
• Types of Alleles
– Dominant alleles – expressed in the
appearance of the trait.
Mendel’s example:
purple flower color
– Recessive alleles –
– Recessive alleles – not expressed when
paired with a dominant allele
– Recessive alleles – not expressed when
paired with a dominant allele
Mendel’s example:
– Recessive alleles – not expressed when
paired with a dominant allele
Mendel’s example:
white flower allele
How did Mendel determine this???
Looking closer at Mendel’s work
Parents
1st
true-breeding
true-breeding
X
purple-flower peas
white-flower peas
100%
purple-flower peas
generation
(hybrids)
100%
self-pollinate
2nd
generation
75%
purple-flower peas
25%
white-flower peas
3:1
Mendel collected data for 7 pea traits
What did Mendel’s findings
mean?
• Some traits mask others
– purple & white flower colors are separate
I’ll speak for
both of us!
traits that do not blend
• purple x white ≠ light purple
• purple masked white
– dominant allele
• Makes functional protein
– affects characteristic
allele producing
functional protein
mutant allele
malfunctioning
protein
• masks other alleles
– recessive allele
• no noticeable effect
• allele makes a
non-functioning protein
homologous
chromosomes
• Genotypes and Phenotypes
• Genotypes and Phenotypes
Genotype– tells what
• Genotypes and Phenotypes
Genotype– tells what types of alleles are
in a pair (dominant, recessive or one of
each).
• Genotypes and Phenotypes
Genotype– tells what types of alleles are
in a pair (dominant, recessive or one of
each).
• Phenotype –
• Genotypes and Phenotypes
Genotype– tells what types of alleles are
in a pair (dominant, recessive or one of
each).
• Phenotype – the appearance of the
trait (ex. – purple flowers or white flowers)
• Genotype
phenotype.
• Genotype determines phenotype.
• How are Genotypes written?
• How are Genotypes written?
– Genotypes are usually two-letter symbols
(one for each allele). The letter used is
usually the first letter of the dominant trait.
• How are Genotypes written?
– Genotypes are usually two-letter symbols
(one for each allele). The letter used is
usually the first letter of the dominant trait.
• Dominant alleles
• How are Genotypes written?
– Genotypes are usually two-letter symbols
(one for each allele). The letter used is
usually the first letter of the dominant trait.
• Dominant alleles are written in capital
letters.
• How are Genotypes written?
– Genotypes are usually two-letter symbols
(one for each allele). The letter used is
usually the first letter of the dominant trait.
• Dominant alleles are written in capital
letters.
• Recessive alleles
• How are Genotypes written?
– Genotypes are usually two-letter symbols
(one for each allele). The letter used is
usually the first letter of the dominant trait.
• Dominant alleles are written in capital
letters.
• Recessive alleles are written in lowercase letters
Types of genotypes:
Types of genotypes:
Homozygous -
Types of genotypes:
Homozygous - when both alleles are the same
Types of genotypes:
Homozygous - when both alleles are the same
Heterozygous –
Types of genotypes:
Homozygous - when both alleles are the same
Heterozygous – when the alleles of a pair are
different
• Example: Purple flower color is dominant
to white flower color in pea plants.
P – purple
p - white
• Example: Purple flower color is dominant
to white flower color in pea plants.
P – purple
p - white
PP –
• Example: Purple flower color is dominant
to white flower color in pea plants.
P – purple
p - white
PP – homozygous dominant
• Example: Purple flower color is dominant
to white flower color in pea plants.
P – purple
p - white
PP – homozygous dominant
pp –
• Example: Purple flower color is dominant
to white flower color in pea plants.
P – purple
p - white
PP – homozygous dominant
pp – homozygous recessive
• Example: Purple flower color is dominant
to white flower color in pea plants.
P – purple
p - white
PP – homozygous dominant
pp – homozygous recessive
Pp -
• Example: Purple flower color is dominant
to white flower color in pea plants.
P – purple
p - white
PP – homozygous dominant
pp – homozygous recessive
Pp - heterozygous
• Genotype / Phenotype examples:
Earlobe trait – Free earlobes – F
Attached earlobes – f
Rabbit fur -
Brown fur – B
White fur - b
Genotypes
FF
Ff
Phenotypes
Free earlobes
attached earlobes
bb
brown fur
Bb
Genotypes
FF
Ff
ff
bb
BB or Bb
Bb
Phenotypes
Free earlobes
Free earlobes
attached earlobes
white fur
brown fur
brown fur
• The Punnett Square
Diagram that can predict the outcome
of cross.
Aaaaah,
phenotype & genotype
can have different
ratios
Punnett squares
Pp x Pp
1st
generation
(hybrids)
%
genotype
male / sperm
female / eggs
P
p
PP
25%
75%
Pp
P
PP
%
phenotype
50%
Pp
Pp
p
Pp
pp
pp
25% 25%
1:2:1
3:1
• Patterns of Inheritance
• Patterns of Inheritance
– Autosomal dominant
• Patterns of Inheritance
– Autosomal dominant
• Trait caused by:
• Patterns of Inheritance
– Autosomal dominant
• Trait caused by: dominant allele on an autosome
• Patterns of Inheritance
– Autosomal dominant
• Trait caused by: dominant allele on an autosome
– Example:
• Patterns of Inheritance
– Autosomal dominant
• Trait caused by: dominant allele on an autosome
– Example: Huntington’s disease
• Patterns of Inheritance
– Autosomal dominant
• Trait caused by: dominant allele on an autosome
– Example: Huntington’s disease
Freckles
• Patterns of Inheritance
– Autosomal dominant
• Trait caused by: dominant allele on an autosome
– Example: Huntington’s disease
Freckles
Widow’s peak
– Autosomal recessive
– Autosomal recessive
• Trait caused by a
– Autosomal recessive
• Trait caused by a recessive allele on an autosome
– Autosomal recessive
• Trait caused by a recessive allele on an autosome
– Example:
– Autosomal recessive
• Trait caused by a recessive allele on an autosome
– Example: Cystic fibrosis
– Autosomal recessive
• Trait caused by a recessive allele on an autosome
– Example: Cystic fibrosis
Albinism
– Autosomal recessive
• Trait caused by a recessive allele on an autosome
– Example: Cystic fibrosis
Albinism
Hitchhiker’s thumb
– Incomplete dominance
• When neither allele is fully dominant
– Heterozygote phenotype is intermediate
– Example: flower color in snap dragons
– Sex-linked Recessive
– Sex-linked Recessive
• Trait caused by recessive allele on the
– Sex-linked Recessive
• Trait caused by recessive allele on the X
chromosome
– Sex-linked Recessive
• Trait caused by recessive allele on the X
chromosome
Example:
– Sex-linked Recessive
• Trait caused by recessive allele on the X
chromosome
Example: color blindness
– Sex-linked Recessive
• Trait caused by recessive allele on the X
chromosome
Example: color blindness
Hemophilia
– Sex-linked Recessive
• Trait caused by recessive allele on the X
chromosome
Example: color blindness
Hemophilia
Muscular dystrophy
Genotypes of sex-linked traits include the
chromosomes:
Genotypes of sex-linked traits include the
chromosomes:
XhXh
Genotypes of sex-linked traits include the
chromosomes:
XhXh
XhY
Genotypes of sex-linked traits include the
chromosomes:
XhXh
XhY
Males get more sex-linked recessive
conditions than females do.
Why???