Hemophilia is an X-linked recessive disorder. The blood of a hemophiliac lacks the ability to clot, due to the fact that one or more of the plasma proteins required to form a clot is absent or reduced in their blood.
A recessive gene, it is carried on the female chromosome X . Males possess XY chromosomes and females XX. Since females have two X chromosomes, they are more often than not carriers.

If you look at the Punnett Square you can see the following.
Each child of a carrier will have a 50% chance of inheriting hemophilia. The daughter of a male haemophiliac will always inherit the disease, while a son cannot ever inherit it. A female will only be affected with haemophilia in the rare circumstance that she inherits mutated X chromosomes from both a hemophiliac father and a carrier mother. No case of such double inheritance is known among Queen Victoria's descendants.
Correction:
1:47 I made a mistake. The H in the lower right box should be lower case h and not a capital letter. H

Learn to add and subtract integers with counters
Using counters is a great way to teach integers to students and a great way to visualize integers when adding and subtracting.
You can use almost anything to represent integer counters.
Paper circles,coins, plastic circles can all be used as counters.

Moon vocabulary In this video, I define,
Waxing Moon
Waning Moon
Crescent Moon
Gibbous Moon
New Moon

Alkaline Earth Metals-- Alkaline earth metals are found in group 2 of the periodic table
They include beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra)
The alkaline earth metals share several common properties, they have
Low density
Silver and soft metals
Ductile and malleable
React with halogens and water
Alkaline earth metals are reactive, not as reactive to alkali metals, but still very reactive. This is because they all contain two electrons in their outer shell. Because they are reactive they are usually found in nature in compound form.

Strontium compounds are often added to fireworks displays for their red flame test color.
Calcium is used by our body for our teeth and bones.
Magnesium is used in antacid and barium is used in light bulbs.
So there are the group 2 alkaline earth metals. They each have two valence electrons.
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What happens when you mix sodium and water?
Hint: It involves fire.
https://www.youtube.com/watch?v=YRPuDQtB_5Y&t=41s

The first stage of mitosis called prophase

In this video, I answer the question, " What makes an insect an insect?
An insect belongs to the phylum Arthropoda and the class Insecta
Insects have an exoskeleton,wings,6 legs, and a segmented body.

Ecological pyramids
Ecological pyramids show how energy is transferred in an ecosystem.
In this video, I cover three types,
pyramid of energy
pyramid of biomass
pyramid of numbers

In this video, I describe the four stages of mitosis, prophase, metaphase, anaphase, and telophase.
During metaphase, the sister chromatids align in the middle of the cell.
However for this to happen a couple of things had to happen during prophase
During prophase, the chromatin condensed into x shaped chromosomes.
Each half of the x is a sister chromatin with identical copies of the DNA
In other words, a sister chromatin is 'one-half' of the duplicated chromosome.
The two sides of the x shaped chromosome is attached at the centromere.
Centromeres are the regions of DNA where the sister chromatids are most tightly connected.
During anaphase, the chromosomes line up in the middle of the cell.
The chromosomes move away from each other during the phase of mitosis called anaphase.
Finally, in telophase, the nuclear membrane reappears and the cell pinches in the middle.

A concave mirror curves inward in the center. In this video, I use a laser to demonstrate ray of incidence, the ray of reflection,focal point,center of curvature, and the vertex

The Equinox is the date in which the day and night are equal. The Solstice is the longest day of the year? Because the Earth is tilted at a 23.5 degrees angle and also rotates and revolves around the earth the length of the day varies though out the year
During each equinox, both hemispheres receive almost equal amounts of sunlight
12 hours of daylight and 12 hours of nighttime.
Questions answered in this video?
What are the dates of the vernal equinox and the autumn equinox?
What are the dates of the summer solstice and the winter solstice?
What is the equilux?
When is the shortest day of the year?
When is the longest day of the year?

Have you ever wondered how you catch a cold? I discuss 5 ways microorganisms spread.
These include direct contact, indirect contact, airborne, oral route, insects and pests.

Learn how to create a stem and leaf plot. A stem and leaf plot is another method for organizing data so you can see patterns.
Draw the Stem and Leaf Chart
Identify the Stem
Sort your data and divide the numbers into a stem and a leaf
Provide a key