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Early Ideas About Heredity
• Combined genetic material from a sperm and an egg determines the traits or features of an offspring.
Early Ideas About Heredity
• The idea of blending inheritance is offspring are a blend of genetic material from both parents.
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Gregor Mendel and His Experiments
• Gregor Mendel was the first to record evidence that traits are determined by factors passed from parents to offspring.
• Mendel established the basic laws of heredity.
Gregor Mendel and His Experiments
• Genetics is the study of how traits of organisms are passed from parents to offspring.
Mendel’s Experimental Methods
• Mendel conducted breeding experiments by studying seven traits of pea plants and each trait had only two variations.
Controlled Experiments
• Mendel controlled fertilization in the pea plants, allowing him to see how traits pass from one generation to another.
Controlled Experiments
• He also performed cross-fertilization by transferring pollen from one pea flower to another.
Mendel’s Unique Methods
• Used true-breeding plants for each trait—plants that always produce offspring with that trait when they self-pollinate
Mendel’s Unique Methods
• Recorded the inheritance of traits for several generations
• Used a mathematical approach
Mendel’s Experimental Results
• Mendel concluded that two factors control each inherited trait.
Plant HeightT (tall)
t (short)
TTttTt
Mendel’s Experimental Results
• When organisms reproduce, each gamete—sperm or egg—contributes one factor for each trait.
orT
T
ort
t
T
t
t
T
or
TT tt Tt Tt
Dominant Factors
• A genetic factor that blocks another genetic factor is called dominant.
• A dominant trait is observed when offspring have one or two dominant factors.
• Indicated by the capital letter (Y for yellow)
Y
YY or Yy
Recessive Factors
• A genetic factor that is hidden by the presence of a dominant factor is recessive.
• A recessive trait can be observed only when two recessive genetic factors are present in offspring.
• Indicated by the lowercase letter (y for green)
y
yy
Modern Definitions of Mendel’s Ideas
• Mendel did not know about DNA or how cells reproduce, but his ideas about inheritance are still true today.
Genes and Alleles
• Each form of a gene with different information is called an allele.
Alleles
• A or a
• D or d
• T or t
Phenotype and Genotype
• The observable traits and all characteristics of an organism make up the organism’s phenotype.
Phenotype and Genotype
• The alleles that make up an organism is the organism’s genotype.
• The alleles of a particular gene is that gene’s genotype.
Homozygous and Heterozygous Genotypes
• Because eukaryotes have pairs of chromosomes, a genotype for a gene has two alleles.
Homozygous and Heterozygous Genotypes
• If the two alleles have the same information, the genotype is homozygous.
Homozygous and Heterozygous Genotypes
• If the two alleles have different information, the genotype is heterozygous.
Symbols
• Y = yellow (dominant)
• y = green (recessive)
• ___ different genotypes & ___ different phenotypes
Genotype Phenotype
YY (homozygous dominant) yellow (purebred)
yy (homozygous recessive) green (purebred)
Yy (heterozygous) yellow (hybrid)
3 2
Mendel’s Law of Segregation
• During meiosis is when gametes (sperm/egg) form.
• The two factors for each trait segregate (separate) from each other during meiosis.
Mendel’s Law of Segregation
• Each set of chromatids separates into different gametes.
• Each gamete receives only one allele.
Mendel’s Law of Independent Assortment
• The factors for one trait separate independently of how factors for other traits separate
Mendel’s Law of Independent Assortment
• A daughter cell might receive the A or a chromosome from pair 1 and the B or b chromosome from pair 2.
Mendel’s Law of Independent Assortment
• This results in four possible allele combinations (for two homologous pairs of chromosomes).
Importance of Mendel’s Genetic Studies
• In the 1860s, no one knew about chromosomes or meiosis so it was hard to understand Mendel’s discoveries.
• All the research of modern genetics is based on Mendel’s conclusions from his work with pea plants.
What is the passing of traits from parents to offspring called?
A inheritance
B genetics
C heredity
D allele
4.1 Foundations of Genetics
What are the alleles that make up an organism called?
A genes
B genotype
C phenotype
D factors
4.1 Foundations of Genetics
If two alleles for a gene have the same information, what kind of genotype does that gene have?
A homologous
B recessive
C heterozygous
D homozygous
4.1 Foundations of Genetics
What is the term for the idea that offspring are a blend of genetic material from both parents?
A polygenic inheritance
B sex-linked inheritance
C maternal inheritance
D blending inheritance
What type of alleles can only be observed in the phenotype when they are present as a homozygous genotype?
A dominant
B recessive
C inherited
D heterozygous
What is the term for the idea that inheritance of one trait is not influenced by inheritance of another trait?
A law of independent assortment
B law of heredity
C law of segregation
D maternal inheritance
Which pea trait did Mendel not study?
A seed color
B pod color
C flower position
D flower shape
SCI 2.c