human genetics

Human Genetics• Phenotype: observed physical and functional traits • Genotype: complete set of genes and alleles • Alleles: Different versions of homologous genes ex... publishing as B

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Human Genetics

• Phenotype: observed physical and

functional traits

• Genotype: complete set of genes and alleles

• Alleles: Different versions of homologous genes ex B and b

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Human genetics

• How are gametes made?

• How does chromosome behavior affect inheritance of traits?

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• Somatic cells are diploid.

• Gametes are haploid, with only one set of chromosomes

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polar body

secondary oocyte

polar bodies (will be degraded) spermatids

meiosis ll meiosis l SPERMATOGENESIS OOGENESIS

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1st law - segregation of alleles

• Cells contain 2 copies (alleles) of each gene

• Alleles separate during gamete formation (meiosis)

• gametes carry only one copy of each gene

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Possible genotypes and

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Law of Independent Assortment

• During gamete formation, genes for

different traits separate

independently into gametes

• Why? random alignment of homologues at Meiosis I

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Figure 9.17

Chromosome behavior accounts for Mendel’s principles

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• Incomplete dominance in human

LDL

LDL receptor

Cell Normal Mild disease Severe disease

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Ex three alleles for ABO blood type in humans

I A , I B , i

Many genes have more than two alleles

in the population

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• Quantitative traits

skin color, height, eye color

Polygenic traits - A single trait may be influenced

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• The inheritance of many

human traits follows

Mendel’s principles and

the rules of probability

Genetic traits in humans can be tracked through family pedigrees

Figure 9.8A

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• Family pedigrees are used to determine patterns of inheritance and individual genotypes

Figure 9.8B

Dd

Joshua Lambert

Dd

Abigail Linnell

D_

Abigail Lambert

Female

Dd

Elizabeth Eddy

D_

John Eddy

Hepzibah Daggett

?

dd Dd

Dd Dd

dd Dd

Dd

Male Deaf Hearing

dd

Jonathan Lambert

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Inherited Genetic Disorders

Dd

Normal (carrier)

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• A few are caused by dominant alleles

Figure 9.9B

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• Most sex-linked human

disorders are due to

recessive alleles

red-green color blindness

These traits appear mostly in males Why?

allele from his mother, he will have the disorder; while a female has to receive the allele from both parents to be affected

Sex-linked disorders affect mostly males

Figure 9.23A

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Pedigree Chart: Inheritance Pattern for an X-linked

Recessive Disease

Figure 19.12

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• A high incidence of hemophilia has plagued the royal families of Europe

Figure 9.23B

Queen Victoria

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Variations on Mendel’s Principles

• Codominance, multiple alleles

• Pleiotropy

• Polygenic traits

• Sex-linked genes

• Environmental effects

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n + 1 n + 1 n – 1 n – 1

Number of chromosomes

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meiosis II

Figure 8.21B

Normal meiosis I

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• An extra chromosome 21 causes Down syndrome

• The chance of having a Down syndrome child goes up

with maternal age

Figure 8.20C

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• Karyotyping and biochemical tests of fetal cells can help people make reproductive decisions

Centrifugation

Fetal cells

Fluid

Uterus Cervix Cell culture

Several weeks later

Karyotyping

Biochemical tests

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• Chorionic villus sampling is another procedure

that obtains fetal cells for karyotyping

Fetal cells (from chorionic villi)

Karyotyping

Some biochemical tests

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• Examination of the fetus with ultrasound is

another helpful technique

Figure 9.10C, D

PGD - Preimplantation Genetic Diagnosis

genetic analysis of embryos from in vitro fertilization (IVF) before inserting into womb

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Genes and Behavior

• Mechanism

phenotypes: hormones, enzymes, transport, neurotransmitters

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