Chapter 12 Human Genetics 1882 Flemming 1887 Weismann 1900


Chapter 12 Human Genetics

1882 Flemming

1887 Weismann

1900 Mendel

Chromosomes and Inheritance


Diploid organisms possess pair of _______________________________, which are alike in length, shape, and gene sequence.


Crossing over between chromosomes results in _____________________________

Independent assortment:

Chromosome’s structure may change during ______________ or ___________________

Section 12.2 (Read it)

Sex Determination

Each human egg will contain 22 _____________________plus one X but sperm will carry 22 autosomes plus either an X or Y

X bearing ___________ plus X bearing _______________ produces female offspring

X bearing egg plus Y bearing _________________ produces male offspring

________Chromosomes obviously codes for sexual traits, but it also carries many genes for nonsexual traits

Y chromosomes carries a _________________ determining (SRY) gene which leads to formation of the ________________________

Absence of the male gene in females results in formation of ____________________

Linked Genes

Linked genes on specific chromosomes are referred to as _________________________

Thomas Hunt Morgan: _________________ experiment confirmed the location on a chromosome

Some of the most intriguing linkage are those of __________________ and


Analysis lead to the result of linkage groups and ________________ locations

Human Genetics

Is very difficult to ______________________

We live in very________________ population and variable conditions

Mate by chance and may or may not choose to__________________

Small family size is not sufficient for meaningful statistical analysis



Provides data on ______________________ through several generations

Knowledge of ______________________ and Mendelian inheritance patterns is used in analysis of pedigrees to yield clues to a trait genetic basis

Human Genetic Disorders

Genetic abnormality-

Genetic disorder-

Genetic disease-.


Autosomal recessive inheritance

Characteristics of this condition are:

Heterozygotes are symptom__________ – Homozygous are _____________

2 Heterozygous parents

50% producing a ________________________

25% ________________________

Galactosemia _____________________

_______________________________ prevents the manufacturing of an enzyme needed in the conversion pathway

Example of a autosomal recessive pedigree


• Cystic Fibrosis

• Phenylketonuria (PKU)

• Sickle Cell Disease

• Cystic Fibrosis

Autosomal Dominant inheritance

The dominant allele is nearly always _________________________ and if it reduces the chance of ____________________________, its frequency should decrease; nonreproductive effects, and postreproductive.

If a parent is heterozygous and other parent is homozgyous recessive there is a 50% chance that any child will be _________________________

Example of






Huntington Disease


X-linked inheritance

Characteristics of this condition are:_______________________________

Males: are:



Hemophilia A :

Fragile X syndrome defective X chromosomes that produces a faulty protein that results in


Some genes are located on the _________________________. Females receive _____________ alleles for these genes, but males only receive one.

When doing a punnet square, use large ___________________ to denote male and female, use

_____________________ letters to designate the alleles

If you are trying to determine if an allele is sex-linked, and which is dominant, a reciprocal cross is performed White eyed male x red eyed female | Red eyed male x white eyed female

X r Y x X R X R | X R Y x X r X r

• Colorblindness Red-green colorblindness makes it difficult for the person to discern the two colors ( test yourself!)

• If the parent is a ___________________, the genotype is automatically known. A colorblind male has to be b, since he only has one allele and colorblindness is recessive. A normal male must then be B

• _______________________ can be heterozygous for the colorblindness trait - they are called carriers. A female can be BB - normal, Bb - carrier, or bb - colorblind

• The following shows a cross between a normal man and a woman who is a carrier.

Muscular Dystrophy



1. What is the chance that a woman with hemophilia will have a child with hemophilia? (What sex would the child need to be?)

2. In a cross where a brown-haired female is crossed with a black-haired male, all the male offspring have brown hair and all the female offspring have black hair. What must be the genotypes of the parents? Which allele is dominant?

3. In drosophila (fruit fly), the allele for eye color is located on the X chromosome, where red eyes is dominant to white eyes. Show the cross of a heterozygous red-eyed female and a white eyed male.

4. A man who is colorblind marries a woman whose father is colorblind. What is the chance that they will have colorblind children?

Read the section on Progeria


Chromosome Changes





Label the chromosome changes

Changes in Chromsome Number



A chromosome number can change during ____________________________ cell division or during the fertilization process

_____________________________germ cells can result if cytoplasmic division does not follow normal DNA replication or mitosis


At __________________ or _________________ frequently results in a change in chromosome number

If gamete with an extra chromosome (n+1) joins a normal gamete at fertilization the diploid cell will be 2n+1, this condition is called _____________________

If an abnormal gamete is missing a chromosome, the zygote will be 2n -1 _________________

Down Syndrome

• Down syndrome results from _______________________

– 1 in 1,100 live births in North America are affected

– _____________________________

– ______________________ Defects

– Frequently occur with women over the age of _________________

Changes in Sex Chromosomes

Turner’s Syndrome

Klinefelter Syndrome