Chapter 3 - The New Genetics Flashcards
Chromosomes
Each chromosome is made of protein and a single molecule of deoxyribonucleic acid (DNA). In humans, each cell contains 23 pairs of chromosomes, for a total of 46.
Genes
the basic unit for transmitting heredity (the passing on of physical or mental characteristics genetically from one generation to another)
Humans have __ chromosomes
46 (23 pairs)
Humans have about __ genes
25,000
Meiosis
the biological process of sex cell division resulting in gametes that have 23 chromosomes, which is half the amount of genetic material normally seen in a human cell. This is because it matches up with the other parents cell.
Mitosis
the biological process of cell division resulting in bodily cells that are exact copies of their parent cells and have a full set of 46 chromosomes.
Gamete
A reproductive cell. A sperm or ovum that can produce a new individual if it combines with a gamete from the other sex to make a zygote
How many chromosomes does a baby get from their mom, and how many from the dad?
23 from each parent
Karyotype
the number and visual appearance of the chromosomes in the cell nuclei of an organism or species.
Autosomes
The first 22 pairs of chromosomes
The 23rd pair of chromosomes are the?
Sex chromosomes
Genotype
ones complete set of genes
phenotype
the actual appearance and behavior of a person, and occurs because some instructions on the genotype are ignored, and others amplified.
What is a polygenic trait?
refers to inherited traits that are influenced by many genes, rather than by a single gene
dominant-recessive pattern
he influence of one gene in the allele is greater than the other gene.
i.e. blood types A and B and brown eyes result from dominant genes.
X-Linked recessive inheritance
a mode of genetic inheritance by which a dominant gene is carried on the X chromosome.
Pairs of alleles can be either ____ or ____
homozygous (same gene) - an individual inherits the same alleles for a particular gene from both parents
heterozygous (different gene i.e. blue from one parent, brown from another) - its cells contain two different alleles of a gene
Dominant allele
its chemical instructions are followed
Recessive allele
its chemical instructions are ignored
Incomplete dominance
one allele doesn’t dominate the other completely. Blending of parental traits. Red Flower / White Flower = Pink Flower
Codominance
One allele doesn’t dominate the other – they co-exist (appear together).
i.e.
Blood Type
What is the difference between incomplete dominance and and codominance?
Blending versus coexisting
What blood types are codominant?
What blood types are recessive?
A allelle and B allele
O allele
Human genome
the code for making a human being
the human genome is __% the same for any 2 people.
95.5%
when does development begin?
at conception, when the sperm penetrates the ovum.
when the sperm penetrates the ovum, what is created?
a zygote
The genotype of the zygote is the?
genetic information on the 23 chromosome pairs.
The blastocyst has a raised area in the middle called the ____ ____
embryonic disc
Zygote duration
Fertilization to 2 weeks
Embryo duration
3 to 8 weeks
Fetus duration
9 weeks to birth
What comes first, Sexual Differentiation or Sexual Determination?
Sexual Determination
Sexual Differentiation
The process of becoming female or male
Sexual Determination
when the maternal and paternal chromosomes join and create zygotes which are either XX or XY
What determines gonadal (testicles/ovaries) sex?
chromosomal sex
depending on what your exposure to the hormones are, a child can either be more or less ____
masculine
What causes behavioral differences (sex wise)?
Morphological Differences in CNS
Effector Differences (muscles)
In mammals, ____ external genitalia is the ‘____’ sex
female, neutral
Additional steps are needed for male external genitalia. What does this mean?
more chances of error
In what ways are we sexually dimorphic?
- size & shape
- physiology
- cognitive function
- behaviour
David Reimer story
David Reimer, an identical twin from Winnipeg whose penis was accidentally removed during a botched circumcision as a baby. John Money, was assigned to his case. His genitals were partially converted to female ones, female hormones were administered and Mr. Reimer was raised as a girl.
David Reimer revealed later, however, that he never felt like a girl. He committed suicide in 2004. His twin brother committed suicide a short time later
Santhi Soundarajan
Has complete androgen insensitivity syndrome (cAIS) (you’re XY, you have testosterone, but you have no receptors in your body - not on your genitals, muscles etc.)
Won silver medal in 2006 Asian Games Was stripped of her medal after failing a sex test
Chromosomal Sex
Most basic level – sex as it is determined by the sex chromosomes that They receive at birth.
Gonadal Sex
The possession of either ovaries or testes
Hormonal Sex
Females of most vertebrate species posses higher levels of estrogen to androgen ratios compared to males; males have the opposite pattern
Morphological Sex
Differences in body type between males and females
i.e. breasts
Behavioural Sex
Male-typical vs female-typical behaviours (females of most species often care for young, males often defend territory)
Homogametic Sex
similarly shaped sex chromosomes – females (XX)
Heterogametic Sex
differently shaped sex chromosomes – males (XY)
Levels of determination
chromosomal sex (determined at conception) ➺ gonadal sex (determines hormonal environment) ➺ hormonal sex (mediates morphological development) ➺ morphological sex (leads to behavioral sex differences) ➺ behavioral sex
Hormonal differentiation
your primordial gonalds either turns into testes or ovaries depending on the sex determining region Y (SRY) gene (found in Y chromosome)
♀
Mullerian
♂
Wolffian Duct
Mullerian inhibiting substance can be seen as?
Spray that removes weeds
How does a male XY develop?
⇝Primordial gonalds develop into testes
⇝Mullerian inhibiting substance causes the mullerian system to wither away
⇝Androgens develop a wolffian system
⇝Primordial external genitilia develops into penis and scrotum
How does a female XX develop?
⇝Primordial gonalds develop into ovaries
⇝Mullerian system develops into fallopian tubes, uterus etc.
⇝Wolffian system without androgens withers away
⇝Primordial external genitilia develop into clitoris, labia and outer vagina
testis determining factor
a protein encoded by the sex determining region Y (SRY) gene
Turners Syndrome
there is partial or complete absence of one of the 2-X chromosomes in a phenotypic female
During the process in which eggs or sperm are formed, one of the sex chromosomes are
lost, an embryo receiving only a Y-chromosome cannot survive, but an embryo receiving
only a X-Chromosome may survive and develop as a female with Turners
Congenital Adrenal Hyperplasia
adrenal glands produce stress hromones, but also androgens
someone with CAH their adrenals produce way too much androgens
Androgen Insensitivity Syndrome - Partial vs. Complete
no receptors or some receptors
Klinefelter Syndrome
Extra x-chromosome
(XXY) – Because the Y gene is present – the sex determining region Y (SRY) gene is expressed and activates masculinization – therefore they are sexed as males at birth (Y causes release of anti mullerian hormone)
Usually sterile because of low sperm production
Penis does not grow, voice does not deepen, breasts may develop
Jocob’s Syndrome
Extra y-chromosome
(XYY) Male at birth, but sterile. Male prisoners have a disproportionately higher rate of XYY
Impaired language skills
Having an extra Y chromosome was thought to contribute to increased aggression/criminal activity (many prisoners have it), was this true?
NOPE: they have lower intelligence and are very tall = easier to get caught and more easily identifiable
Perinatal androgens most common cause of abnormal sexual differentiation
- Endogenous (within the body)
- Exogenous (i.e. Bisphenol A (BPA) has fidoestrogen which means it mimics estrogen)
rats couldn’t get pregnant when they drank from plastic water bottles which has BPA
disrupts female system
and introduces high levels of estrogen into their system)
Additivegenes
combine to make a phenotype.
The inherited genes from mother and from father are added together. However, some additive genes get enhanced by other genes, making their input greater.
i.e. Curly hair, skin colour, height
Dizygotic (fraternal) twins
result from two sperm penetrating two ova, and share 50% of their genes.
Monozygotic (identical) twins
originate from one zygote, and share 100% genes.
How are monozygotic twins made?
- early embryo splits before implanting in womb
- early embryo implants in womb and then splits
- early embryo implants in womb and then splits later
What do you need for dizygotic twins?
- 2 chorions
- 2 amnions
The likelihood of multiple births vary by ____ and
____
age and ethnicity
Why are we more likely to have twins as we age?
We tend to hyper-ovulate
Do identical twins run in the family?
No
Highest and lowest rates of twins?
Highest: Africa
Lowest: Asia/South America
Hazards of multiples include:
birth complications, low birth weight, death, disease, and disabilities.
Genes have been found to influence several disorders, including:
What else plays a key role in these disorders?
Schizophrenia
Addiction
Nearsightedness
Diabetes
Environment
Chromosomal abnormalities
when the zygotes cells have fewer or more chromosomes than 46.
What is the most common correlate of chromosomal abnormalities?
Maternal age
Older mother = older ova
Down syndrome
when a zygote has 3 copies of chromosome 21 (a trisomy)
Sufferers experience mental slowness, faster aging, and physical problems.
Down syndrome is also known as
Trisomy 21
Huntingtons disease
a fatal CNS disorder caused by a genetic miscode. It is inactive until middle adulthood
Tourette syndrome
a dominant disorder, can lead to uncontrollable tics and obscenities.
Genetic counseling provides facts. It is recommended for:
– Couples from the same ethnic group
– Individuals with a close relative with a genetic condition
– Couples with a history of infertility or miscarriage
– Women 35 or older, men 40 or older
Zygote
is the single cell formed from the union of two gametes, a sperm and an ovum
Deoxyribonucleic Acid (DNA)
A material present in nearly all living organisms as the main constituent of chromosomes. It is the carrier of genetic information
Allele
a variation that makes a gene different in some way from other genes for the same characteristics. Many genes never vary, others have several possible alleles
Epigenetics
the study of how environmental factors affect genes and genetic expression
Genome
the full set of genes that are instructions to make an individual member of a certain species
What sex chromosome is bigger with more genes?
X
Vanishing twin phenomenon
when you see 2 embryos at first, but only 1 continues to grow
Infertility
failure to conceive a child after a year of trying
Subfertile
when a couple is less fertile than ideal but not sterile
Both sexes become less fertile every year starting at age __. Who has a deeper decline?
18, women
Almost every trait is ____ (affected by many genes)
polygenic
Recessive genes are not apparent unless the child happens to inherit the same recessive gene from?
Both parents
____ are more likely to be carriers of X linked traits but are less likely to express them
females
What leads to a recognizable syndrome?
If an entire chromosome is missing or added
Characteristics if Trisomy 21?
Thick tongue
Round face
Slanted eyes
Distinctive hands/feet/fingerprints
Hearing problems
Heart abnormalities
Muscle weakness
Short stature
Two rules that must be followed by genetic councillors
Tests are confidential
Decisions are made by clients
Blastocyst
Bundle of cells into which a fertilized ovum divides
adrenal glands produce stress hromones, but also androgens
someone with CAH their adrenals produce way too much androgens
What is this called?
Congenital Adrenal Hyperplasia
